Record, of Ihe We,lcm Allslrallan MlI'ClIlI1 20: 167--185 (2001).

The earliest Cambrian Polyplacophorans from China

YuWen

NanJing In,titute of C;eology and Palaeontology, Chmese Academy of Sciences, NanJmg, 210008, ChmaPresent address: Department of Earth and Planetary Sciences, Western Australian Museum,

FranCls Street, Perth, Western Australia 6000, Australiaemail: wen.yu88@hotmail.com

Abstract Restudy of Yllnnanoplellra, Tchallg,ichiloll, RlIllllegaroc!lIloll,Mel,hllcllnchllon, Yanglzechiloll and LlIyanhaochitoll from the earliest Cambrian1I1 the Yangtze Region of China confirms the appearance of thePolyplacophora in the earliest Cambrian. It also suggests an origin for theclass m late Proterozoic. Yallgtzcchiton and Lllyallhaochitol1, represented 111 thestudy material, are typical polyplacophorans having head, intermediate andtail valves, each with a tegmentum and an articulamentum. Thesemorphologic features establish their distinction from the non-molluscangenus Paracarmachitc,. The polyplacophoran character of species of the generaYlInllanoplclIra, Tchallg,ichiton, Meishllclll1chiton and Gotlalldocl1llol1 7 isdemonstrated by the presence of discrete areas (central or jugal, lateral) onthe mtermediate valves. YWlIlal10plcllra is probably ancestral to the EarlyOrdovlclan Chelodes Davidson and King. RlIl1l1egarochiton appears to b~'

related to the Middle Ordovician Pn,cochilon Dall.

INTRODUCTION

The Yangtze Region is one of the areas in Chinawhere the Lower Cambrian is most developed. Ithas been studied in great detail, with the locationof type sections for series division and stagesestablished. During the past 30 years, as a resultof ongoing research on the Proterozoic-Cambrianboundary strata, a great number of molluscs havebeen discovered from the Meishucun Stage ofeastern Yunnan, western Sichuan, western Hubeiand southwestern Shaaxl. They are especiallysignificant from the Meishucun section of Jinningand the Baizai section of Xundian, Yunnan(Figure 1).

The Meishucun Stage of the Yangtze Region isdominated by a micromolluscan fauna. The faunacontains a diversity of primitive forms ofpolyplacophorans, merismoconchs, bivalves,stenothecoids, rostroconchs, hyoli ths, tergomyans,helcionellids and gastropods Among these fossils,the appearance of primitIve Polyplacophora in thepre-trilobite and pre-archaeocyathid stage isparticularly significant (Figure 2).

The writer has described two polyplacophoransfrom the earliest Cambnan, elollgatllsYu (1984a, plate 1, figures I Yu 1984b, text-figure4a-€) and SPlI/lIS Yu (1984a, plate 1,figures 8, 9; Yu 1984b, text-figure 4f-g). In 1987, thewriter reported further earliest Cambrianpolyplacophorans, incJudmg YlIIllwllOplellra blfor1l1isYu (1987b, plate 17, figures 1--8; plate 18, figures 1-9;text-figure 43), TclulIIgsiclliton notabilu, Yu (1987b,

plate 4, figures 1-10; text-figure 33), 5inllconus clypeusYu (1979, plate 1, figures 10-13; 1987b, plate 5,figures 1-11), RW1I1egarochiton 1110destlls Yu (1987b,plate 6, figures 1-6; text-figures 13, 35),Meishunll1chitol1 vulgarus Yu (1987b, plate 15, figures4-10; text-figures 36, 37), Postestephaconus tentes Jiang(1980, plate 1, figures 10-13; Yu 1987b, plate 7,figures 1-11; text-figure 38), 5tolic01lUS vol11eres Jiang(1980, plate 1, figure 2; Yu 1987b, plate 5, figures 12­13; plate 6, figures 7-10; text-figure 39) andGotlandochitol1? l11inil11us Yu (1987b, plate 15, figures1-3; plate 16, figures 1-8; text-figure 42). Smith andHoare (1987: 3) listed Yangtzechiton elongatlls Yu andLlIyanhaochiton spinus Yu as representatives of theEarly Cambrian Polyplacophora_ Haszprunar (1988:402) has pointed out, "It is argued that the fossilrecord of the Polyplacophora starts much later thanthat of the Conchifera. However, in the light of recentfindings of tiny Polyplacophora from the lowestCambrian (Yu, 1987), this argument must beabandoned".

Some scholars have lumped Yanglzechiton andLlIyanlwochitoll under Paracarillacllllcs (Kerber, 1988:187). Qian and Bcngtson (1989: 48) have stated: "Wecannot accept Yu's (1984a, 1984b, 1987)interpretation of and LlIyallhaochilonas polyplacophorans. As shown below, both ofthese generic names are Junior synonyms ofParacarillaclllles .. _" .

On the other hand, He and Xie (1989: 126)considered that Paracarillacllltes has a long platewith spines, possibly representing the dorsal shield

168

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Figure 1 Map showing important localities of the earliest Cambrian polyplacophorans in Yangtze Region of China.

of an animal. It was their view that Yangtzechitonmight be the shells of primitive animals belongingto the Polyplacophora. Salvini-Plawen (1990: 2)wrote: "Moreover, the Precambrian and EarlyCambrian Placophora described by Yu (1987) fromChina were like-wise small (1.2 mm-5 mm) ...".Morris (1990: 76) clearly stated that theMeishucunian contains a rich fauna of chitons,equal to any locality today. Peel (1991: 5) stated:"During the last decade fused associations ofminute sclerites have been described from theearliest Cambrian of China and interpreted asmicrochitons (Yu, 1987, 1990). These have beenseized upon as the missing early polyplacophoranlink in molluscan evolution (e.g. Haszprunar, 1988;Yu,1990)".

In the same year, Conway Morris and Chen (1991:384, plate 8; text-figure 10) agreed with Qian andBengtson's viewpoint. Rurmegar (1996: 82) stated"the earliest known chitons are not Runnegarochitonand its associates but instead are species of Mattheviafrom the latest Cambrian of the United States".

The writer is firmly of the view that Yangtzechitonand its related genera belong to the ClassPolyplacophora, and that the affinities ofParacarinachites remain to be clarified (Yu, 1987b,1990, 1993, 1996). During the last few years, therehave been some exciting contributions on Cambrianfossils. Triplicatella disdoma Conway Morris, 1990

from the Lower Cambrian Parara Limestone andAjax Limestone of South Australia (Bengtson et al.1990) was reinterpreted as the earliest knownpolyplacophoran by Yates, Gowlett-Holmes andMcHenry (1993: 71). Chen et al. (1995) recognizedYunnanozoon lividum Hou, Ramskold andBergstrom, 1991 as the oldest chordate recordedfrom the Maotianshan Shale Member of the LowerCambrian Yu'anshan Formation of Chengjiang,Yurman, China (Chen et al., 1995).

There has also been new work on thePrecambrian. Molecular test results of Wray et al.(1996) suggested that invertebrates includingechinoderms, arthropods, annelids and molluscsdiverged from chordates about a billion years ago,about twice as long as the Phanerozoic. One of thenon-mineralized Ediacaran fossils, Kimberellaquadrata (Glaessner and Wade 1966), from the Ust'­Pinega Formation of the Winter Coast of the WhiteSea in northern Russia, was reinterpreted byFedonkin and Waggoner (1997) as a mollusc-likefossil. Zhang et al. (1998) indicated thatpermineralized fossils from the terminal ProterozoicDoushantuo Formation of South China, includingthe large animals, radiated into a world rich inprokaryotic, protistan and even multicellulardiversity which existed just before the Ediacaranradiation. The origin of shelled chitons within thelate Proterozoic is in accord with the likely

Earliest Cambrian Polyplacophorans 169

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170 YuWen

Earliest Cambrian Polyplacophorans

evolutionary history of the Phylum Mollusca.Early Cambrian YllIzgtzecllitoll and related genera

possess some peculiar structures and they bear avery close evolutionary relationship to youngerchitons.

What has been mentioned above indicates thatpolyplacophorans had already begun to diversifyby the beginning of the Early Cambrian However,Qian and Bengtson placed these polyplacophoransin synonymy with other small shelly fossils, andthey are jumbled together with their taxa (Qian andBengtson, 1989, 1992a, b; Qian, 1989, 1993;). TIle aimof this paper is to discuss how to distinguish earlypolyplacophorans from other small shelly fossIls inthe earliest Cambrian.

Illustrated specimens are housed in the NanjingInstitute of Geology and Palaeontology, ChineseAcademy of Sciences, Nanjing, People's Republic ofChina.

WHY YANGTZECHITON AND RELATEDGENERA ARE POLYPLACOPHORANS

Qian and Bengtson (1989: 49) concluded that thereis no basis for the claim to polyplacophoranaffinities of 'Yallgtzeclziton' or 'Luyanlzaochiton', andthat both are synonyms of Paracarinachites. Thepresent writer finds Qian and Bengtson's conclusionto be incorrect for the following reasons:

The polyplacophorans, or chitons, generally havea series of eight overlapping plates or valves,situated dorsally, and held in place by a toughmuscular girdle, which may be either naked orvariously ornamented with spicules, scales, bristles,or hairy protuberances (Smith, 1960). In Yangtze­clliton elongatus Yu, the holotype comprises a headvalve and two intermediate valves (Yu, 1984a, plate1, figures 1-5; 1987a, plate 1, figures 1-4; 1987b,plate 8, figures 1-4, plate 9, figures 1-3, plates 10­12; 1990, plate 2, figures 1-3, plate 3, figures 1-5;1993, plate 1, figures 1-2; Figures 3A-F); theparatype is composed of four intermediate valvesand one tail valve (Yu, 1984a, plate 1, figures 6··-7;1987b, plate 8, figures 5-7, plate 14, figures 1-4;

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1990, plate 2, figures 4-5; 1993, plate 1, figures 3-4;Figure 4A-B), and the third figured specimen hast\'\'o intermediate valves (Yu, 1987a, plate 1, figure5; 1987b, plate 9 figure 4; Figure 4C). In the otherspecimens there are six overlapping valves (Qianand Bengtson, 1989, figure 29A; Qian, 1993, plate Il,figure A; Figure 5). In Luyallhaochiton spill us Yu, theholotype is composed of a head valve and threeintermediate valves (Yu, 1984a, plate 1, figures 8-9;1987a, plate 1, figures 6-7; 1987b, plate 13, figures1 plate 14, figures 5-6; 1990, plate 2, figures 6-8;1993, plate 1. figures 5-6; Figure 4D-E) and thefigured specimen has two intermediate valves (Yu,1987a, plate 1. figure 8; 1987b, plate 13, figure 6). Sofar as I know, no other chitons with such wellpreserved shells have been recorded from theCambrian. The earliest hitherto fossilpolyplacophoran remains (generally separatevalves) occur in the Upper Cambrian and have beenfound sparingly in rocks of all geological ages(Smith, 1960). In most, the full complement of head,intermediate, and tail valves has not been found(Smith and Hoare, 1987).

The shells of polyplacophorans are generally 25­75 mm in length and occasionally up to 43 cm in thelargest one known. However, the shells of thosediscovered from the earliest Cambrian of theYangtze Region are only 3-5 mm in length, and justover 5 mm in the largest one. Although theseprimitive chitons are very tiny, they possess thebasic features of the Class Polyplacophora. Smith(1960) indicated that head and tail valves usuallydiffer in shape from each other and from the sixintermediate valves, the latter commonly beingmuch alike in contour. Like modern chitons, theshell of Yallgtzechiton elongatus is composed of threedifferent shapes of valves: the head valve is nearlyas long as wide, without a raised hole (Figure 3A­B), anterior margin broadly rounded, posteriormargin with a broad and deep sinus; theintermediate valve is longer than wide, with one­half of the valve overlapped by the preceding one,the middle of the anterior part has an elliptical hole,which may be the result of a hollow spine falling

...... Figure 3 A-F. Yangtzechiton elongatlls Yu, A Dorsal view of shelly fossil, showing head and intermediate valves, x 90B. Enlargement of the head and mtenneciIate valves, showing the granules and spicules (white arrow) x 195C. Enlargement of spicules on the dorsal Side of the intermediate valve, x 900. D. Ventral view, showing thecontiguous fissures between mdivldual valves (white arrow), x 70. E. Ventral view of the head valve,showing the nephroid depreSSion, fIssure and other structures (white arrow), x 135 F. RIghtlateral view, showing the one-half of an mtermediate valve overlapped by the preceding one (white arrow),x 110. Holotype. NICP 84131 Coil no KM-7. Upper part of Zhongyicun Member of Lower Cambnan

on£vlt1£ Formation. Melshucun of E Yunnan. C-K. Paracarinilchites sincnsis Qian and Jiang, CDorsal view, alternately and nodular projections, x 120. H. Enlargement of nodularprojections and expansively overturned \entral margin in adapical curved part, x 250. L Ventral VIew,showing a subcircular dish with an openll1g in Its subcentre (white arrow), x 80. J. Lateral view, showingmany thin lamellae arranged parallel to each other (white arrow), x 65. K. Enlargement of thin lamellar(white arro\'v), x 170. NICP 101908. Col] no XB-40. Upper part of Zhongyicun Member of Lower CambrianTongying Formation. Baizai of Xundian, E. Yunnan.

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Earliest Cambrian Polyplacophorans

off; and the tail valve is long and arched,rectangular, with subcentrally located mucro(Figure 4A-B). In Luyallhaochitoll spillus the headvalve is much wider than long, the anterior marginis semicircular, and there is no hollow spine; theintermediate valves differ from the head valve inthe presence of a hollow spine, the basal part of thespine is broadly rounded and extends toward andinserts into the preceding valve, connecting theanterior valve with the posterior one (Figure 4D-E).111e tail valve is unknown.

The surface of the intermediate valves is usuallymarked off by a diagonal line or rib into threetriangular areas, one median and two lateral(Hyman, 1967). YUl1l1al1opleura biformis Yu isdistinctly divided into three areas: a large centralarea, roundly convex, occupying most of thedorsum and ornamented with coarse to finetransverse ribs; and two lateral areas which aresmall, subtriangular, distinct in its dividing linefrom the central area, omamented with 10-12 stoutoblique ribs, and with one of the ends intersectingthe transverse ribs in the central area at 40° (Yu,1987b, plates 17-18; 1990, plate 4; Figure 8 H-N).Gotlal1dochitoll? mil1imus is obviously divided intojugal and lateral areas. Jugal area rounded andconvex, jugal sinus broadly concave, U-shaped;lateral area separated from jugal area by a stout,rounded ridge extending from near the apex toanteriolateral margin (Yu, 1987b plate IS, figures1-3; plate 16, figures 1-8; Figure 9 L-P). Theintermediate valves of the Tchal1gsichitol1 IlotabilusYu (Figure 8 A-G), Postestephacollus telltes Jiang(Figure 8 O-R) and Meishucul1chitol1 vulgarus Yu(Figure 9E-I), are weakly divided into three areas.

Although Yal1gtzechitol1 and related genera areprovided with some peculiar structures, they bear a

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very close evolutionary relationship to youngertaxa. Ywmal10pleura having a long valve and anapical hole, probably gave rise to Chelodes Davidsonand King (1874), frequently found from the EarlyOrdovician (Bergenhayn, 1960; Runnegar et al.,1979) to Silurian (Figure 6D-F). MeishucUllchitoll issimilar to Eochitoll Smith (1964) from the LowerOrdovician of southern Oklahoma; RUllIlegarocllitollis closely related to Priscocllitoll Dall (1822) from theMiddle Ordovician of Canada in the outline of theintermediate valve and in the presence of arecurved tegmentum (Figure 6J-L). Yallgtzechitonbears some resemblance to the genus Glyptochitol1de Koninck (1883) from the Lower Carboniferous ofBelgium (Figure 6P-Q), in the possession of a broadsinus at the posterior margin of the head valve, theintermediate valves are longer than wide andbearing a concave hole, though they are rather farfrom each other in geological age. Luyal1haochitol1 isanalogous to the chitons of the later Paleozoic in themorphology of the shell, but in this genus, theanterior end of the intermediate valve is possessedof an obliquely backwardly directed hollow spinewhich makes it different from other known genera.Finally, Gotlandochiton? minimus Yu is similar toGotlandochiton troedssol1i Bergenhayn from theSilurian of Sweden (Bergenhayn, 1955, plate I,figure 9; plate Il, figure 7; Figure 6N).

These examples demonstrate that Yangtzechitonand related genera not only represent primitiveforms of the major polyplacophoran groups thatevolved after the Early Cambrian, but they alsorepresent the initial diversification of the ClassPolyplacophora. This discussion on theevolutionary relationships of polyplacophoransfurther confirms that CR. Stasek's prediction hasbeen realised in the Chinese fossil collections: "The

..... Figure 4 A-C. Yangtzechiton elongatlls Yu, A. Dorsal view of shelly fossil, showing intermediate valves and tail valve,x 120. B. Right lateral view, showing the one-half of an intermediate valve overlapped by the preceding one,x 105. NIGP 84132 Coil. no. KM-7. Upper part of Zhongyicun Member of Lower Cambrian TongyingFormation. Meishucun of Jinning, E. Yunnan. C. Dorsal view of two intermediate valves, x 60. NIGP 84133.ColI. no. XB-28. Upper part of Zhongyicun Member of Lower Cambrian Tongying Formation. Baizai ofXundian. E. Yunnan. D-E. Lllyanhaochiton spin liS Yu, D. Dorsal view of shelly fossil, showing head andintermediate valves, x 80. E. Left lateral view, showing the anterior part of the spine extending and insertinginto the preceding valve, x 80. Holotype. NIGP 84135. ColI. no. KM-7. Upper part of Zhongyicun Member ofLower Cambrian Tongying Formation. Meishucun of Jinning, E. Yunnan. F-P. Paracannachites sinensis Qianand Jiang, F. Dorsal view, showing nodular projections and expansively overturned ventral margin in theadapical part and alternately arranged spines in the posterior part, x 50. G. Enlargement of the adapical part,showing the nodular projections, x 80. H. Lateral view, x 40. NIGP 101902. Coil. no. XB-40. 1. Dorsal view, x55. J. Lateral view, x 30. NIGP 101901. ColI. no. XB-28 K. Lateral view, x 24. Cat. no. 10362 (ChengduInstitute of Technology, Sichuan). Upper part of Zhongyicun Member of Lower Cambrian TongyingFormation. Yulu of Huize, E. Yunnan L-M. Longitudinal sections, showing the thin lamellar arrangedparallel to each other, x 30, and x 120. Cat. no. 10356 (Chengdu Institute of Technology, Sichuan). Upper partof Zhongyicun Member of Lower Cambrian Tongying Formation. Meishucun of Jinning, E. Yunnan. N.Ventral view, showing adapical curved part with a subcircular dish and widely concave posterior part, x 35.O. Enlargement of subcircular dish, x 150. NIGP 101909. ColI. no. XB-28. P. Ventral view, showing adapcialpart with a subcircular dish and widely concave posterior part, x 70. NIGP 101916. Coli. no. XB-28. Upperpart of Zhongyicun Member of Lower Cambrian Tongying Formation. Baizai of Xundian, E. Yunnan.

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cFigure 5 Yangtzechiton elongatus Yu, A. Dorsal view of shelly fossil, showing intermediate valves. B. Left lateral view,

shoWing the one-half of each intermediate valve overlapped by the preceding one. C. Ventral view, shoWingthe continguous fissues between individual valves, x 50, NIGP 106887, (after Qian and Bengtson, 1989: 53).

chiton fauna of the Upper Carnbrian was probablythe result of a very early and separate trend frommuch smaller ancestral forms whose remains havenot yet been found or recognised" (Stasek, 1972: 12).

A COMPARATIVE STUDY OFYANGIZECHITON YU AND

PARACARINACHlTES QIAN AND JIANG

Comparisons were made between a greatnumber of samples (more than five hundredspecimens) were collected by the writer and hiscolleagues from the Baizai section in Xundian andthe Meishucun section in Jinning, Yunnan in 1980.On the 11th June, 1981, the writer picked for thefirst time from an acid-residual sample, an earliestCambrian polyplacophoran with the head valveand intermediate valves overlapping together. Thiscame from the Lower Cambrian ZhongyicunMember of Tongying Formation of the Meishucunsection of Jinning. The writer gave this informationto Liu Di-rong and Qian Yi and introduced to themthe locality, horizon and the morphologicalfeatures of the Lower Cambrian Polyplacophora,as well as outlining the essential significance of theresearch on these fossils.

In 1984, Qian published on the Lower Cambrianpolyplacophorans Carinac1tites spinatus andParacarinachites sinensis. However, Qian's publisheddescriptions and illustrations of presumed EarlyCambrian polyplacophorans were not molluscs; hemistakenly regarded Carinachites spinatus Qian(1977: 265, plate III, figures 17-19) andParacarinachites sinensis Qian and Jiang 1982 (in Luoet al., 1982: 183, plate 17, figure 17) as members of

the Class Polyplacophora (Qian, 1984a: 93, plate I,figures 26-28; plate Il, figures 14-16, 23-24; 1984b:18, figures I, 37-1, 38).

As previously noted (Yu, 1987b, 1990, 1993), theshell of Yangtzechiton elongatus is composed of ahead, intermediate and tail valves. The intermediatevalves consist of tegmentum and articularnentum,longer than wide, with one-half of the valveoverlapped by the preceding one, and with anelliptical hole in the middle of anterior part, whileParacarinachites is an elongately curved sclerite, thewhole composed of many thin lamellae arrangedparallel to each other, and with 15-20 nodularprojections and spines alternately arranged on theouter side.

The description of Paracarinachites sinensis (Qianand Bengtson, 1989: 49) centres around the scleriteformed by growth increments overlapping eachother on the inner surface towards the abapical end.From the description and illustrations in He andXie (1989, plate 1, figures 11-12); Qian andBengtson, (1989, figures 27-28), and Yu (1993, plateI, figures 10-11), it is clear that P. sinensis iscomposed of many thin lamellae arranged parallelto each other.

Along the middle of the dorsal surface of chitons,there extends a longitudinal series of eight, usuallyoverlapping valves (Hyman, 1967). Overlappingrefers, in particular, to the form of the shell in thePolyplacophora. In general, the posterior valve isusually overlapped by the preceding one. Sclerites,on the other hand, have been described by Qianand Bengtson (1989: 51): "The sclerites have aclearly laminated structure (Figure 27A3),suggesting that they are built up of superimposed

Earliest Cambrian Polyplacophorans

E

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Figure 6 Diagrams showing that the earliest Cambrian Polyplacophorans bear a very closely evolutionary relationshipto younger taxa. A-e. YllIwanopleura biformis Yu, x 20. NIGP 84173. Zhougyicun Member of Lower CambrianTongying Formation, Baizai of Xundian, E. Yunnan. D-F Chelodes bergmani Davidson and King, x 2. MiddleSilurian of Gotland, Sweden (after Davidson and King, 1874). G-I. Rllnnegaroclziton modestus Yu, x 20. NIGP84161. Zhongyicun Member of Lower Cambrian Tongying Formation, Meishucun of Jinning, E. Yunnan. J-L.Priscoclziton canadensis (Billings), x 4. Middle Ordovician of Ottawa River, Canada (after Smith, 1960). M.Gotlandoclziton? minimus Yu, x 32.5. NlGP 84155. Zhongyicun Member of Lower Cambrian TongyingFormation, Meishucun of Jinning, E. Yunnan. N. Gotlandoclziton troedssoni Bergenhayn, x 4.6. Silurian ofGotland, Sweden (after Smith, 1960). O. Yangtzeclziton elongatus Yu, x 35. NlGP 84131. Zhongyicun Memberof Lower Cambrian Tongying Formation, Meishucun of )inning, E. Yunnan. P-Q. Glyptoclziton cordifer deKoninck, Lower Carboniferous of Belgium (after Smith, 1960).

growth layers. TI1e apical end of several specimenshas a characteristic build-up of laminae (Figure 28)that also appear to represent successive growthincrements". In fact, P. sinensis is built-up of six ormore parallel arranged lamellae (Qian andBengtson, 1989, figure 28; Figures 4L-M, 7B-C).TI1erefore, the present writer concludes that theseauthors have not distinguished between themeaning of the words 'overlapped' and'superimposed'.

In Yangtzechitoll elongatus, the ventral side of thehead valve has a nephroid depression near theanterior margin, with a series of W-shaped curvedstriae in the posterior part of the depression; theintermediate valves are slightly concave on the

ventral side, with contiguous fissures betweenindividual valves clearly visible (Yu, 1984a, plate1. figure 3; 1987a, plate 1, figure 2; 1987b, plate 8,figure 2; 1990, plate 2, figure 2; 1993, plate 1, figure2; Figure 3D-E). In Paracarinadlites sinellsis, thelower side of the sclerite is divided into two parts:the adapical curved part with a subcircular dishbearing an opening in its subcentre, and posteriorpart widely concave (Qian, 1984a, plate I, figure27, Yu, 1993, plate 1, figures 8-9,12-14; Figure 31,4N-P).

The number and arrangement of the spines ordenticles also serve to distinguish betweenYallgtzechiton and Paracarinachites. In Yallgtzechitonelollgatlls, the head valve is small, without a raised

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Figure 7 A-C. Paracarinachites sinensis Qian and Jiang,A. Lateral view, x 30, NIGP 70939 (after Qian,1984a). B-C. Lateral and ventral views, x 60,NIGP 106886 (after Qian and Bengtson, 1989).D. Paracarinachites bispinosus He and Xie,dorsal view, x 37.5, NIGP 106896 (after Qianand Bengston, 1989).

has a raised hole, which may be the result of ahollow spine falling off (Yu, 1984a, plate 1, figures1,4,6-7; 1987a, plate 1, figures 1,3,5; Figure 3A-B;4A-C), while in P. senensis, the outer surface of thesclerite bears 5-6 nodular projections in theadapical curved part and 10-15 alternatelyarranged spines in the posterior part (Yu, 1987b,1990, 1993; He and Xie, 1989; Figure 3G-H, 4F-K).But Qian and Bengtson (1989: 51) considered that"The largest number of denticles observed is 10". Intheir illustration the denticles usually number 10 or

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less, due to the incomplete specimens. However,years earlier Qian described a well-preservedspecimen of P. sinensis, which has at least fifteenspines alternately arranged on the dorsal side (Qian,1984a, plate 1, figure 28, NIGP 70939; Figure 7A).

In the diagnosis of the genus Paracarinachites, Qianand Bengtson (1989: 49) stated: "Outer surface withregularly spaced denticles, usually inclined towardsthe abapical end of the sclerite". The publishedillustrations of many specimens of P. sinensis (Heand Xie, 1989, plate 1 figures 8-10; Qian andBengtson, 1989, figure 27: Yu, 1993, plate 1, figures7, 10, 15-18) clearly show the denticles alternatelyarranged on the dorsal side with their tips obliquelybackward and inclined leftward (or rightward). In1989, a new species Paracarinachites bispinosus Heand Xie (1989, plate 1, figures 13-15) (=P. parabolicusQian and Bengtson, 1989, figures 30-31) wasdescribed from the Lower Cambrian Dahai Memberof the Tongying Formation of Huize, Yunnan. Thisspecies has two rows of spines on the dorsal side,their tips aligned obliquely leftward (or rightward)and backward (Figure 70), similar to those of P.sinensis. These characteristics fully demonstrate thatthe diagnosis of the genus Paracarinachites and thedescription of P. sinensis provided by Qian andBengtson (1989) does not fully reflect the precisefeatures of the species, P. sinensis.

In this monograph, Qian and Bengtson claim thatYangtzechiton Yu and Luyanhochiton Yu, are bothjunior synonyms of Paracarinachites Qian and Jiang(Qian and Bengtson 1989: 48-54, 102-103).Conway Morris and Chen (1991: 382-385, 393­394), Bengston (1992b: 408), Bengston and ConwayMorris (1992: 461, 467) and Qian (1989: 265; 1993)repeated the same view. From the abovecomparisons, it is clear that Yangtzechiton andLuyanhaochiton are both valid taxa and that theybelong to the Class Polyplacophora.Paracarinachites is no more than a single sclerite.The multivalved and univalved form is a major

Figure 8 A-G. Tchangsichiton notabilus Yu, A. Dorsal view of an intermediate valve, shOWing the central and lateral ~

areas and broadly U-shaped jugal sinus, x 65. B. Ventral view, showing the deep concave central area, x 80.Holotype. NIGP 84140. ColI. no. TF-l. C. Dorsal view of an intermediate valve, showing aesthetes, x 60.NIPG 84141. ColI. no. TF-1. D. Dorsal view, showing the sculptures, x 70. E. Ventral view, x 55. F. Posteriorview, x 40. NIGP 84142 ColI. no. TF-l. G. Dorsal view of the tail valve, x 60. NIGP 84143. ColI. no. TF-l.Upper part of Huangshandong Member of Lower Cambrian Tongying Formation. Tianzhushan of Yichang,W. Hubei. H-N. Yunnanopleura biformis Yu, H. Dorsal view of an intermediate valve, showing the central andlateral areas (white arrow), x 30. I. Ventral view, showing the apical area with several rows of nodularprojections, x 35. J. Left lateral view, showing the lateral and central areas (white arrow) x 35. K. Enlargementof the central and lateral areas, showing different kinds of the sculptures in the central and lateral areas, x80. Holotype. NIGP 84173. ColI. no. XB-52. L. Left lateral view, showing lateral and central areas (whitearrow), x 35. NIGP 84172 ColI. no. XB-52. M-N. Ventral views, showing the V-shaped apical area and otherstructures, x 30 and x 60. NIGP 84174. ColI. no. XB-52. Upper part of Zhongyicun Member of LowerCambrian Tongying Formation. Baizai of Xundian, E. Yunnan. O-R. Postestephaconus tentes Jiang, O. Dorsalview of an intermediate valve, showing the central and lateral areas (white arrow), x 90. NIGP 84206. ColI.no. XB-28. Upper part of Zhongyicun Member of Lower Cambrian Tongying Formation, Baizai of Xundian,E. Yunnan. P. Right lateral view, x 85. Q. Dorsal view, showing bluntly rounded apex and lateral area (whitearrow), x 90. R. Enlargement of apex and lateral areas x 180. NIGP 84209. ColI. no. KM-7. Upper part ofZhongyicun Member of Lower Cambrian Tongying Formation. Meishucun of Jinning, E. Yunnan.

Earliest Cambrian Polyplacophorans 177

178 YuWen

Earliest Cambrian Polyplacophorans

character used in high level classification. Qianand Bengtson's treatment of Yangtzcchiton andLlIyanlzaoclziton as junior synonyms ofParacarinaclzitcs, is at variance with the basicconcepts of biological taxonomy.

ON THE DIFFERENCES BETWEENOCRURANUS LIU AND

RUNNEGAROCHITON YU

Qian and Bengtson (1989) discuss some otherpolyplacophorans from the Meishucun Stage, inwhich certain genera and species of the genusOcrllranlls Liu are lumped together. However,before discussing the classification of these fossils, itis necessary to make clear the generic characteristicof Ocrllranlls. The genus was erected in 1979 by Liu,taking OCnlranus finial Liu as the type species (Liu,1979, plate 1, figure 3; Figure 90). The genericdiagnosis given (Liu, 1979: 506) as follows: "Outlinenearly conical; hinge line straight and wide;pseudointer area high, nearly procline;pseudodelthyrium round-convex and complete,without foramen pedicle. Surface with concentricgrowth striates".

Liu (1987: 376-377) later supplemented thegeneric characteristics of Ocruranlls as follows:"Shell small, slightly bilaterally asymmetrical, withsemiconical ventral and dorsal valves in roughmirror symmetry; ventral interarea procline, whiledorsal one small, nearly catacline; homeodeltidiumconvex and well-developed, but with no foramenseen; surface with only a small number ofconcentric bands; shell microstructure consisting ofalternate sparse and dense thin layers of flakes".The amended generic diagnosis of Ocrural1l1s is used

179

for discussion of the problems with in Qian andBengtson's taxa.

Rrl1llJcgarocIlitolJ Yu, 1987 is a polyplacophoranwith R. modcstlls Yu as the type species. Acomparison of R. modcstlls with the Ocru ran 115 finialLiu shows their essential difference. In R. 1ll0dcstlls(Yu, 1987b, plate 6, figures 1-6, Text-figures 13,35;1990, plate 1, figures 3-6; Figure 9A-C), theintermediate valve is subtriangular in dorsal view;the tegmentum is recurved onto the ventro­posterior portion of the valve, forming a V-shapedhole below the apex, with its margin extendingdownward and then inversely curved outward,forming a recurved plate (Figure 9B-C). InOcrurmms finial (Liu, 1979, plate 1, figure 3; Figure90), the shell is subcircular, ventral valvesemiconical, pseudointer area high and procline,pseudodelthyrium roundly-convex, but with novisible foramen; dorsal valve low-conical, apexrounded and slightly curved, situated posterior!y,interarea low (Liu, 1979: 506).

Rrml1cgaroclziton modestus is also easilydistinguished from Ocrural1l1S slIbpentacdrlls (Jiang)(1980: 117, plate I, figures 6, 9, 14), because theshell of O. slIbpcntacdrus is generally rounded toovoid in outline and has a more or less straightproximal edge. The apex is situated close to theproximal margin. The subapical field is set off by amore or less pronounced furrow. A characteristicfeature is the re-entrant at the proximal margin,which may form an acute angle and extend to theapex, or be less pronounced, resulting in a highersubapical field. The apical part together with thethickened rim of the subapical re-entrant arecommonly preserved as isolated fragments (Qianand Bengtson, 1989: 106).

..... Figure 9 A-C RlIIlIlegarochiton modestlls Yu. A. Dorsal view of an intermediate valve, x 30. B. Ventral view, showingthe V-shaped apical area and recurved plate, x 30. C. Left lateral view, showing the recurved plate on theventral side, x 50. Holotype. NIGP 84161. ColI. no. KM-7. Upper part of Zhongyicun Member of LowerCambrian Tongying Formation. Meishucun of ]inning, E. Yunnan. D. Ocrllranlls finial Liu, ventral valve,external view, x 30. Holotype NIGP 57926. CoIl. no. AB-21. Upper part of Zhongyicun Member of LowerCambrian Tongying Formation. Meishucun of ]inning, E. Yunnan. E-1. Meisllllcll11chiton ulIlgarlls Yu, E.Dorsal view of an intermediate valve, showing the central and lateral areas (white arrow) x 50. F. Rightlateral view, x 85. G. Left lateral view, x 60. Holotype. NIGP 84191. ColI. no. XD-2. H. Dorsal view, showingthe slightly raised apex (white arrow), x 50. NIGP 84193. ColI. no. XD-2. Upper part of Zhongyicun Memberof Lower Cambrian Tongying Formation. Xianfeng of Xundian, E. Yunnan. I. Right lateral view, showing theslightly raised apex, x 50. NIGP 84194. ColI. no. XB-40. Upper part of Zhongyicun Member of LowerCambrian Tongying Formation Baizai of Xundian, E. Yunnan. ]-K. Eohalobia diandongensls Jian, J. Dorsalview, x 60. K. anterior view, x 55 NIGP 84233. ColI. no. XB-28. Upper part of Zhongyicun Member of LowerCambrian Tongying Formation. Baizai of Xundian, E. Yunnan. L-P. GotlandochUon 7 minimlls Yu, L Dorsalview of an intermediate valve, arched Jugal area, narrow lateral area and broadly U-shaped

sinus. M. Ventral of the ventral valve, x 185. Holotype. NICP 84155 .. O. Dorsal valve, x 40, NICP 84145. ColI. no. KM-7. P. Dorsal view, x

100. NICP 84158. CoiL no. of Zhongyicun Member of Lower Cambrian TongyingFormation. Meishucun of E. Q-S. Ocruranlls slIbpentaedrlls Uiang), Q. Dorsal view, x 65.N!CP 101918. CoIL no. 5-7 Upper part of Zhongyicun Member of Lower Cambrian Tongying Formation.Shangsuan of ]inning, E. Yunnan. R. Dorsal view, x 50. S. Lateral view, x 70. NICP 101917. ColI. no. XB-28.Upper part of Zhongyicun Member of Lower Cambrian Tongying Formation. Baizai of Xundian, E. Yunnan.

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c

B

A

Earliest Cambrian Polyplacophorans

OTHER POLYPLACOPHORANS

As to the classification of Stolicol1l1S V011ll'rcs Jiang(1980, plate 1, figure 2; Figure 10L-M) andPostcstcpl1acol1l1s tel1tl's Jiang (1980, plate 1, figure 13;Figure 80-R) the problem is not as simple as Qianand Bengtson (1989: 103-106; Bengtson, 1992a: 416­417) suggested. It cannot be solved by attributingthese taxa respectively to the species OcntriwlIsfil1ial Liu and O. slIbpcl1tacdrlls (Jiang). Thespecimens of O. slIbpcl1tal'drus obtained from theZhongyicun Member of the Shangsuan PhosphorusMine section in Jinning, Yunnan are abundant andare preserved relatively mtact. More research isnecessary to understand the classification of thesegroups.

Mcisl1l1CZiI1clzitol1 Vu, 1987 was established with M.vlIlgarlls Yu (1987b, plate 15 figures 4-10: Figure 9E­I) as the type species. Its generic diagnosis is asfollows: "Shell very small, elongate, possibly belongto vermiform polyplacophorans. Intermediate valvesheart-shaped, slightly wider than long. Anteriormargin narrowly rounded. Latero-posterior cornerobtusely rounded; posterior margin with a mediansinus. Tegmentum weakly divided into central andlateral areas; central area widely convex, occupyingmost part of the dorsum, with a slightly raised apex;lateral areas small, subtriangular. Margin of valvewith a narrow marginal edge. Head and tail valvesunknown." (Yu 1987b: 110-111). This genussomewhat resembles Eocl1ztol1 Smith (1964) from theLower Ordovician of southern Oklahoma. It is easilydistinguished from the latter by the heart-shapedintennediate valves and smaller lateral areas.

At a glance, Ml'islzllcziI1cl1iton vlIlgarlls Yu (Figure9E-I) appears similar to EoJwlobia diandongcl1sisJiang (Jiang in Luo ct aI., 1982, plate 21, figures 5-6;Vu, 1987b, plate 66, figures 1-11; Figure 9J-K) indorsal view, but the differences are: (1) InMcislzllClil1clziton vlIlgarus, the intermediate valve isnearly heart-shaped in dorsal view, while inEolzalobia diandongcl1sis, it is elongately round orsubovate. (2) In Meisl1l1czil1clziton vlIlgarlls, the dorsalside is divided into central and lateral areas, while

181

in Eolzalobia dimzdol1gel1sis it is undifferentiated. (3)In McislzllcziI1cJliton vlIlgarlls, the apex is slightlyprotruding, while in Eol1alobia diamlongl'nsis, it isbluntly rounded. Here the intermediate valve, withits dorsal side divisible into different areas asobserved in McislzllCZiI1clzilol1 ()lIlgarus, indicates anessential characteristic of the Polyplacophora.

It must be pointed out that the writer (Yu, 1987b)established McislzllClI1ZcJlilol1 Z'lIlgarus Vu, but it ismisspelt as "McisJWClil1COl1l1S" Z'lIlgarus Vu, in Qianand Bengtson's monograph (1989: 108).McislzllCZI1lCOnlls was established by Jiang (1980)with McisI1I1ClI1ZC0111/S c(lJ)zpylllrus Jiang as the typespecies. It represents another group entirelydifferent from Meislzllc1I1zclzil011, and therefore theyshould not be lumped together.

GotlandocIzitOl1 7 mini11l1lS Yu (1987b, plate 15,figures 1-3; Figure 9L-P), an element frequentlyseen in Bed 7 of the Meishucun section, is regardedby some authors as mere fossil fragments. However,the specimens are similar to the intermediate valvesof extant Polyplacophora, because in these valvesthe dorsal side is obviously divided into the jugaland lateral areas, with jugal sinus broadly concaveand V-shaped, indicating that these valves areundoubtedly polyplacophorans and unrelated toOcnmwlIs sllbpentacdrlls (Jiang) (Qian and Bengtson,1989; Bengtson, 1992(1).

IINKENITES - A WONDERFUL FOSSIL

Yu (1988, plates 1-2; Figure lOA-D) described thewell-preserved earliest Cambrian fossil ]inkeniteszl1aoi. However, In Qian and Bengtson'smonograph, ]inke11itcs zJwoi Yu is also attributed tothe genus Canopoconlls Jiang, 1982 (Jiang in Luo eta!., 1982: 193; Qian and Bengtson, 1989: 89;Bengtson, 1992a: 403). In fact, JiJ1kenitcs represents afossil animal with several anterior marginal spinesand peculiar spines on the dorsal side and isentirely different from the genus CanopocoJ1!1S Jiang.

Noting that Bengtson (1992a: 403-404)reconsidered CmlOpOCOJ1!1S Jiang 1982 as a junior

~ Figure 10 A-D jlllkcllItcs :haol Vu, A. Apical view, showing anterior marginal spmes and different kinds of dorsalx 40. B Oblique apical view, x 50. C. Enlargement of anterior margmal x ]80 D Enlargement

. spmes in the posterior part of the body, x 300. Holotype NlGP Coil no. HF-] Upperpart ot 1Iuang.shando.~1gMember of Lower Cambrian Tongying Formation Huangshandong of Yichang, W.Hubel I>H. Pllrcll17 Qlan and Bengtson, E. Anterior view, x 3D I' Lateral Views, x 75. NIGP]019]9 Coil no. XB-28 C Lateral view, x 60. H Apical view, x 40 NICP 10]920 Coil no XB-40 Upperpart of Member of Lower Cambrian Tongving Formation. Balzal of Xundlan, E Yunnan. I-KPllrclla tUlII:lwshiJIlCIISIS Yu, I. Dorsal view, a strongly elevated dorsal and the cancellated

(white arrow), J. dorsal View, showing the dorsal ndge, x 80 K Lateral View, x 55.. . NICP 54453 ColI. no. TF-] part of Buangshandong Member of Lower Cambnan Tongying

Formation 1lanzhushan of Yichang, Bubel L-M. StOliCOlIlIS uOl1lcrcs Jlang L Lateral view, x 75. M.Dorsal vievv, x 75 NIGP 84225 CoIL no. KM-7 Upper part of Zhongyicun Member of Lower CambrianTongying Formation. Meishucun of Jinning, E. Yunnan. N-O. SillllCOlIlIS Yu, N. Dorsal view of anmtermedlate valve, x 72. 0 Posteral view, x 40. NIGP 54408 Coil no. HF-2 Upper part of BuangshandongMember of Lower Cambrian Tongying Formation. Huangshandong of Yichang, W Bubel

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I

Yu Wen

Qiongzhusi Fonu.lliun (14·15)

Sm~---

IT

A B cFigure 11 Paracarinachites sinensis Qian and Jiang. The collection number of Sample A, x 27 (NIGP 106878) and B, x 30

(NIGP 106882) are 159a. They are collected from Section I (after Qian and Bengtson, 1989, p. 8). Thecollection number of sample C, x 40 (NIGP 89505) and sample D, x 20 (NIGP 89575) are YXX-4. They arecollected from Section II (after Qian, 1989, p. 11).

synonym of Maikhanella Zhegallo (Zhegallo inVoronin et al., 1982), then a further likely synonymof Maikhanella calvata (Jiang) (Jiang in Luo et al.,1982: 193, plate 21/ figure 1; Qian and Bengtson,1989: 91/ figure 57) is "Purella" squamulosa Qian andBengtson (1989/ figure 61; Bengtson, 1992a: 410;Figure lOE-H). Judging from the smooth, roundedapical region and the scaly-surface pattern, there isno great difference between "Purella" squamulosaand Maikhanella calvata (Jiang). A great number ofspecimens indicate that they belong to the samegenus and possible species, and are different fromPurella. The latter was established by Missarzhevsky(1974: 184)/ with Purella cristata Missarzhevsky asthe type species. The Chinese species Purellatianzltushanensis Yu (1979: 253, plate 3, figures 18­19; 1987a, plate 3, figures 14-15; 1987b: 189, plate37, figures 6-9, Text-figure 56; Figure 10I-K) isclosely related to P. cristata Missarzhevsky (1974,plate 23, figures 3-5) from the Lower CambrianTommotian Stage of Siberian Platform, but differsfrom the latter in the more bluntly rounded dorsalridge, in the steeper subapical surface and in havingspiral lines. However, in the undeveloped dorsalridge, smooth and rounded apex and theimbricating scale-like protrusions, "Pu rella"

-------

squamulosa is quite different from Purella cristata andP. tianzhusltanensis, but closely resembles thesefeatures of the genus Maikhanella.

SOME COMMENTS ABOUT THE FOSSILLOCALITIES AND HORIZONS IN QIAN AND

BENGSTON/S 1989 MONOGRAPH

All the fossils described in Qian and Bengtson'smonograph were provided by Qian alone. Thefossils were collected from the Meishucun sectionof Jinning and Baizai section and Xianfeng sectionof Xundian by Yu/ Qian and others in 1980.However, in the collection, those fossils from theMeishucun section are labelled from beds 3-13,while all of the specimens from bed 10 of theXianfeng section bear only one collection number159a in their monograph. Among the 57 speciesunder their description, 36 species were collectedfrom the Meishucun section, while the remaining21 species are from only the Xianfeng section. The36 species from Meishucun section include 9species, such as Archiasterella cf. pentactina Sdzuy,Allonnia? tetratltallis (Jiang), A. erromenosa Jaing,A.? simplex Jiang, Halkieria stenobasis (Jiang),Sirzosacltites flabelliformis He, Lapwortltella rete Vue,

Earliest Cambrian Polyplacophorans

Tannuolina zhangwentangi Qian and Bengtson andColeoloides typicalis (Wakott) which have alsobeen found in the Yu'anshan Member of theChiungchussu Formation. The remaining 27species separately yielded from the Zhongyicun,Dahai and Badaowan Members of the TongyingFormation. The 21 species from Xianfeng sectionbearing the collection number 159a are allcollected from the Zhongyicun Member of theXianfeng section (Figure 11, section I). Thepresent writer has some doubts about the localityand horizon of the collection number 159aspecimens.

The Xianfeng section, one of the importantsections in eastern Yunnan, is near the Damaidivillage, about 23 km west of Xundian County. Therethe writer and Qian together systematicallycollected the samples (Coll. No. XD 1-4; X =Xundian, D = Damaidi village), based on the studyof previous authors, without personally measuringthe section. The section has been measured by manypeople, who collected much material, using glacialacetic acid treatment on the matrix. Some fossilshave been extracted from the ore, but only a few arewell preserved. This is because the massivephosphorites in the Zhongyicun Member aremedium-bedded, compact and solid. However, finefossils from number 159a are shown in Qian andBengtson's monograph.

The Baizai section is located about 1 km west ofBaizai village which is about 10 km north ofXundian county. This section is a test pit numberedTC 101, where the slopes on both sides are coveredwith dense vegetation, and the outcrops are verypoor. The basal part is composed of argillaceousdolomite; the dolomitic massive phosphorus rocksof the Zhongyicun Member are extremely loose dueto strong weathering. Among the material, whichwas collected by the writer and Qian, andaccompanied by Wang Chong-wu and Xu Chong­jiu of the First Geological Survey Team, GeologicalBureau of Yunnan Province in December 1980 (Coll.No. XB 1-52; X =Xundian, B =Baizai village), somesamples are rather porous, from which very wellpreserved fossils can be obtained simply by soakingand washing with water, especially specimens ofYunnanopleura biformis Yu, Archaeospira ornata Yu,Yangtzespira exima Yu and Paracarinachites sinensisQian and Jiang. As far as I know, the specimensfrom the Baizai section are the best preserved onesin eastern Yunnan and in the Yangtze Region.

Qian (1989) published another monograph inwhich he described 117 species of small shellyfossils. Among them, 19 species were collectedfrom the same section of Xianfeng PhosphoriteQuarry in Xundian (Figure 11, Section II). Qian(1989, p. 11) wrote: liThe Xianfeng section (Text­figure 5) is located at the Xianfeng PhosphoriteQuarry, 23 km. west of Xundian, Yunnan was

183

mapped out in 1981 by Wang Zhao-bi et al. andrevised by the writer". Huang Zhao-bi (1986),however, is misspelt as Wang Zhab-bi by Qian inQian and Bengtson's (1989) and Qian'smonographs (1989). Most small shelly fossils alsooccur in the bed 10, the collection number is YXX-4(Y = Yunnan, X = Xundian, X = Xianfengphosphorite Quarry, it may be equal to Yu's XD-4)but not collection number 159a in Xianfeng section.The contrast of the fossils between the labelled159a and those labelled YXX-4 is obviouslydifferent, especially as some of the same specieswere collected from the same horizon in the samesection; the features of the fossils are not alike. Forexample, the species Paracarinachites sinensis, withcollection number 159a are very beautiful andwell-preserved (Qian and Bengtson, 1989, figures27-28; Figure llA-B), while the collection numberYXX-4 is very poor in preservation (Qian, 1989,plate 44, figures 1-3; plate 45, figures 9-10; plate48, figures 1-3; Figure llC-D). In addition, thesame results show clearly in the species Scoponodusrenustus Jiang, Paragloborilus subglosus He andCyrtochites pinnoides Qian, etc. What is more,among the plentiful specimens studied by thewriter, Yunnanopleura biformis Yu, Archaeospiraornata Yu, Yangtzespira exima Yu andParacarinachites sinensis Qian and Jiang are mainlyfound in the upper part of the ZhongyicunMember in the Baizai section while thosespecimens obtained from other sections are poor.Judging from the preservation of the fossils andother aspects, it is reasonable for the writer toconsider that Qian's 159a specimens represent amixed fauna, which comprises not only thosefossils from Xianfeng section, but also morespecimens probably from the Baizai section.

ACKNOWLEDGEMENTS

The author expresses his thanks to Lu Yan-Haoand Zhang Wen-tang of Nanjing Institute ofGeology and Palaeontology, Chinese Academy ofSciences, to Luitfried Salvini-Plawen of Institut fUrZoologie der Universitat Wien, Austria, to RichardD. Hoare of Bowling Green State University, USA,to E.L. Yochelson of National Museum of NaturalHistory, Washington D.e, and to K.J. McNamara, J.A. Long and G.W. Kendrick of the WesternAustralian Museum for critically reading themanuscript with valuable suggestions andappreciates the use of museum facilities, to Uu Di­Yong for providing a photograph of Ocruranus finialUu; to He Tinggui who kindly supplied thelongitudinal-section photographs of Paracarinachitessinensis Qian and Jiang; thanks also to Mao Zhi-qianfor preparing the photographs and to Ren Rugao,Danielle West, Anne Nevin, Yu you-yu and MinBridson for their technical assistance.

184

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Manuscript received 23 June 1999; accepted 7 April 2000.