128 



L.R.M. COCKS AND ZHAN REN-BIN 



Shan States, has a smooth shell, a mostly sessile spondylium and a 

 short median septum originating near the anterior end of the 

 spondylium, all of which are typical of Syntrophopsis Ulrich & 

 Cooper ( 1 936: 630). Among the 1 2 species recognized by Ulrich & 

 Cooper (1938) withmSyntrvphopsis, S. laevicula (p. 233, pi. 50, figs 

 22-28), from the West Spring Creek Formation (late Arenig) of 

 Oklahoma, U. S. A., is most similar to our specimen, but without 

 more material, particularly the dorsal interior, no further identifica- 

 tion is possible. 



Family PORAMBONITIDAE Davidson, 1853 

 Genus PORAMBONITES Pander. 1830 



Porambonites spp. 



PI. 5, figs 8-9 



Material and localities. One individual, SMA 3133, with 

 conjoined valves from Sedaw (about 15 km northwest of Kyaukme) 

 and one ventral internal mould, B 29671, from Lebyaungbyan 

 (about 7 km west of Maymyo), both from the Naungkangyi Group of 

 the Northern Shan States. 



DESCRIPTION. Subquadrate dorsi-biconvex shell. Straight hinge 

 line about two-thirds of shell width, round cardinal extremities; 

 maximum width at mid-length. Dorsal fold originating from the 

 umbo; ventral sulcus starting at about mid-length and widening 

 anteriorly to two-thirds shell width. Uniform costellae 4 per mm 

 near the anterior margin. Thin, high and subparallel dental plates to 

 about 40% of shell length; a low transverse ridge connecting their 

 two anterior ends forming a sessile pseudospondylium. 



DISCUSSION. Williams et al. (1965: H532) accepted P. interme- 

 dins Pander ( 1 830) as the nominate type species but pointed out that 

 P. reticulatus Pander (1830) represents the distinctive characters of 

 this genus. The specimens from Burma have some crucial features of 

 Porambonites, i.e., the outline, sulcus and the sessile 

 pseudospondylium in one specimen. The individual illustrated and 

 recognised by Reed (1906: 68, pi. 5, figs 15, 15a, 15b) as P. 

 intercedens Pander, from the same locality and horizon as ours, has 

 a globular outline, weaker fold and sulcus, and denser radial orna- 

 mentation. P. sinuatus Reed (1915: 14, pi. 3, figs 4-5). named on the 

 basis of a ventral valve from the Upper Naungkangyi Group at Man- 

 ngai of the Northern Shan States, has a much deeper sulcus and a pair 

 of divergent dental plates. Reed (1936) also recognised two species 

 from rocks corresponding to the Naungkangyi Group in the South- 

 ern Shan States. P. cf. acutiplicata Reed from Konleau (Reed 1936: 

 48, pi. 3, figs 1-2) has a much more transverse shell with compara- 

 tively shorter hinge line and deeper sulcus originating from the 

 umbo and might also be referred to Porambonites sp. The true 

 acutiplicata Reed (1917: 68, pi. 22, figs 10-11) from Girvan, 

 Scotland, is more circular with a longer hinge line. P. cf. wahli 

 Heinrichson from Ye-o-sin (Reed 1936: 49, pi. 3, fig. 15) has a more 

 circular shell, a weaker fold and much denser costellae, which is 

 very similar to Heinrichson's true wahli (1932: 159, pi. 2, figs 1^1) 

 from the Caradoc of Estonia, so Reed's identification is suitable in 

 the absence of more material. Specimens of P. triquetrus Xu, Rong 

 & Liu (1974: 153, pi. 66, figs 34-35) from the Shihtzupu Formation 

 (early Caradoc) at Zunyi, Guizhou, South China, are very similar to 

 our material except for their shorter hinge line and weaker fold and 

 sulcus. As mentioned under the indeterminate clitambonitid above, 

 the two specimens illustrated as Clitambonites cf. squamata by 

 Reed (1906: 66, pi. 5, fig. 14) and Clitambonites cf. ascendens by 

 Reed (1936: 31, pi. 3, fig. 14) may also represent a species of 



Porambonites, but it appears to be a different species from our 

 illustrated specimens and also from P. sinuatus. In summary, there 

 are not enough Naungkangyi specimens of Porambonites to identify 

 the species with confidence, and it appears that there may be three or 

 even more different species in our material. 



Superfamily LISSATRYPOIDEA Twenhofel. 1914 



Family PROTOZYGIDAE Hall & Clarke, 1893 

 Subfamily PROTOZYGINAE Hall & Clarke, 1893 



Genus PROTOZYGA Hall & Clarke, 1893 



Protozyga? haydeni Reed, 1936 



1936 Protozyga haydeni Reed: 51, pi. 4, fig. 12. 



Discussion. Although there are no atrypoids in our new material, 

 a distinctive dorsal valve from rocks corresponding to the 

 Naungkangyi Group at Taunggyi in the Southern Shan States, was 

 illustrated by Reed (1936: 51) as Protozyga haydeni. This was 

 reassessed by Copper ( 1 986: 834) as P. ? haydeni Reed and we agree. 

 In addition. Reed also figured a single pair of external moulds ( 1 936: 

 52, pi. 5, figs 9-10) from the same locality and horizon as P.? 

 haydeni which he identified as Protozyga? cf. obsoleta Foerste, but 

 which we consider unidentifiable. 



Subfamily CYCLOSPIRINAE Schuchert, 1913 

 Genus CYCLOSPIRA Hall & Clarke. 1893 



Cyclospira sp. 



71932 Hyattidina sp. Reed: 206, pi. 3, figs 17-18. 

 1936 Cyclospira? sp. Reed: 52, pi. 4, fig. 13. 



Discussion. Reed (1936) figured a ventral valve as Cyclospira? 

 sp. from rocks corresponding to the Naungkangyi Group at Taunggyi 

 in the Southern Shan States. Although Reed's identification queried 

 the genus, it appears from Reed's figures that the specimen should be 

 included within Cyclospira. Ventral and dorsal valves from rocks 

 corresponding to the Naungkangyi Group at Taunggyi, Southern 

 Shan States, figured by Reed ( 1932) as Hyattidina sp., might also be 

 included here. 



Acknowledgements. We thank A.H.G. Mitchell and B.J. Amos for the 

 new collections, which they presented to the Natural History Museum, and to 

 R. B. Rickards for the loan of material from the Sedgwick Museum, Cam- 

 bridge. ZRB acknowledges a grant from the Academia Sinica to undertake 

 the work at the Natural History Museum. Thanks to P. Crabb, NHM Photo 

 Unit, for photography. 



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 Bender, F. 1 983. Geology of Burma. 293 pp. Beitrge zur Regionalen Geologie der Erde, 



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