126 



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



LAV 



LI 



Ll/L 



Wl 



Wl/V 



1.01 



13.2 



0.55 



9.2 



0.39 



1.00 



10.8 



0.46 



8.8 



0.37 



1.00 



8.9 



0.43 



7.8 



0.38 



three ventral valves are measured here. 



L W 



BB37606, ventral valve 23.9 23.7 



BB37607, ventral valve 23.7 23.6 



BB37619, ventral valve 20.6 20.5 



Discussion. A dorsal valve (Reed 1936: 69, pi. 3, fig. 6) was 

 identified as Rafinesquina cf. alternata Conrad and a ventral valve 

 (Reed 1936: 70, pi. 3, fig. 7) identified as R. cf. semiglobosina 

 Davidson; both were from the Bawzaing Horizon (equivalent to the 

 Naungkangyi Group) of Sinchaung, Southern Shan States: both are 

 similar to our present material. R. alternata, the type species of 

 Rafinesquina from the Hudson River Group (Caradoc) at Cincinnati, 

 Ohio, U. S. A., differs from the Burmese material in having a larger 

 shell, much less differentiated but denser costellae, and less im- 

 pressed ventral muscle field, as well as the generic differences 

 mentioned above. The true semiglobosina (see Reed 1917: 869, pi. 

 12. figs 13-20) has cardinalia of Type A and well-developed dorsal 

 transmuscle ridges and has been reassigned to the furcitellid 

 Dactylogonia by Williams (1962: 201) and Cocks (1978: 120). So 

 we propose a new species globosa for our specimens, in which we 

 provisionally include Reed's two exteriors. 



The specimens illustrated as Rafinesquina imbrex Pander by Reed 

 (1906: 52, pi. 5, figs 9-12), from the Naungkangyi Group at 

 Tawmawgon in the Northern Shan States, have cardinalia ofType A, 

 well-developed dorsal muscle-bounding ridges and a strong median 

 septum, and so they are within the subfamily Furcitellinae. The 

 dorsal exterior identified as Rafinesquina cf. richardsoni Reed by 

 Reed (1936: 37, pi. 3, fig. 9), from the rocks corresponding to the 

 Naungkangyi Group at Hpongyi Kyaung in the Southern Shan 

 States, differs from our new species in having a much more trans- 

 verse shell and denser costellae. Compared with the true richardsoni 

 (Reed 1917: 868, pi. 12, figs 11, 11a, 12) from the Whitehouse 

 Group (Caradoc) at Shalloch Mill, Girvan, its ornament is more 

 differentiated and denser, although they are similar in shell outline. 

 Since no internal moulds are available, the specimen has not been 

 reidentified here. 



Subfamily LEPTAENINAE Hall & Clarke, 1894 



Indet. leptaenines 



PI. 5, fig. 4 



Discussion. One exterior (BB37744), from the Li-lu Formation 

 (equivalent to the Upper Naungkangyi Group) at Ta-Pangtawng 

 (about 10 km east of Longtawkno), Northern Shan States, has well- 

 differentiated parvicostellae with 6-8 finer costellae between two 

 coarser ones, evenly populated growth lines 1 8 per mm, and concen- 

 tric rugae, and appears to be a leptaenine. Two specimens from the 

 Naungkangyi Group at Ledet and Lebyaungbyan (about 7 km west 

 of Maymyo), Northern Shan States, identified by Reed (1906: 55, pi. 

 4, figs 39^41) as the new species Leptaena? ledetensis, have stronger 



and fewer coarse costellae which cut through all the concentric 

 rugae, and a distinctive ventral interior, so ledetensis should prob- 

 ably be reassigned to some other genus, possibly outside the 

 Rafinesquinidae. Reed (1936) also identified three species of 

 Leptaena, all on the basis of single specimens from rocks corre- 

 sponding to the Naungkangyi Group in the Southern Shan States. 

 The specimen Reed (1936: 33, pi. 3. fig. 3) called L. cf. juvenilis 

 Opik has undifferentiated costellae and strong concentric rugae 

 which bend suddenly posteriorly at a sharp re-entrant angle in the 

 valve centre, but the true juvenilis from Estonia (Opik 1 930: 173, pi. 

 11, figs 140-141; pi. 12. figs 142-145) has parvicostellae and 

 concentric rugae not bending in the middle: however. Reed's Bur- 

 mese specimen might be assigned to Leptaena (Leptaena). The 

 Leptaena cf. richmondensis Foerste of Reed ( 1 936: 34, pi. 3, fig. 11) 

 is a ventral valve which is different from Foerste's true richmondensis 

 (1909: 21 1, pi. 4, figs 10A, B) from the Waynesville Formation of 

 Madison, Indiana, U.S.A., in having a different shell outline, well- 

 differentiated parvicostellae and less developed concentric rugae. 

 We also assign it toLeptaena (Leptaena), but it is not certain whether 

 or not the various Burmese specimens belong to the same species. 

 Leptaena spectata Reed (1936: 34, pi. 3, fig. 12). from the 

 Naungkangyi Group of Taungtala, Southern Shan States, is founded 

 on a single distorted ventral internal mould although it is similar to 

 our specimen in ornamentation: but we cannot properly characterise 

 Reed's species without more material, and thus leave the one or 

 more leptaenine species from the Naungkangyi Group in open 

 nomenclature. 



Family GLYPTOMENIDAE Williams, in Williams et al, 1965 

 Subfamily GLYPTOMENINAE Williams, in Williams et al., 1965 



Genus GLYPTOMENA Cooper, 1956 



Glyptomena sp. 



PI. 5. fig. 6 



Discussion. A single concave dorsal valve (external and internal 

 mould, BB37586). from the equivalents of the Upper Naungkangyi 

 Group at Linwe (Locality AM78), Southern Shan States, has a pair 

 of small, discrete and sessile cardinal process lobes with straight 

 socket ridges fused directly onto their lateral bases, which is typical 

 of Glyptomena. Little can be seen on the external and internal 

 moulds except for the cardinalia. 



Superfamily PORAMBONITOIDEA Davidson, 1853 

 Family SYNTROPHOPSIDAE Ulrich & Cooper, 1936 



Indet. syntrophopsid 



PI. 5, fig. 7 



Discussion. One slightly distorted ventral valve ( BB3769 1 ). from 

 the equivalents of the Upper Naungkangyi Group at Loke-pyin 

 (about 14 km southeast of Ye-ngan, Locality AM 106). Southern 



PLATE 5 



Figs 1-3, 5 Di rafinesquina globosa gen. et sp. nov. Linwe, Locality AM78. la-d, BB 37619, latex cast, and anterior, ventral and posterior views of ventral 



internal mould, x 2. 2a, 2b, BB 37606. posterior and ventral views of ventral internal mould, x 1.5. 3. BB 37612. ventral internal mould, x 5. 5. BB 



37604, ventral internal mould, showing the muscle field, x 2. 

 Fig. 4 Indeterminate leptaeninid. BB 37744, Ta-Pangtawng, Locality YA454.1, latex cast of dorsal exterior, x 2. 



Fig. 6 Glyptomena sp. BB 37586, Linwe. Locality AM78, 6a-c, latex cast and internal mould of dorsal interior, and dorsal external mould, x 3, x 2. x 2. 

 Fig. 7 Indeterminate syntrophopsid. BB 37691, Loke-pyin, Locality AM106, latex cast and internal mould of ventral interior, x 5. x 10. 

 Figs 8-9 Porambonites spp. 8. B 29671. Lebyaungbyan, ventral internal mould, x 1.5. 9a, 9b, SMA 3133. Sedaw. ventral and dorsal views of conjoined 



valves, x 1.5. 



