160 



M. MOHANTI AND C.H.C. BRUNTON 



Fig. 15 Isopoma orthoglossa (Torley). Lectotype; dorsal, ventral, anterior 

 and lateral views (with ventral valve uppermost); Flinzkalk, Givetian, 

 Iserlohn, SMF XVII 1164a, x 2.5 (from Schmidt, 1951: pi. 1, fig. 6). 



Isopoma nekhoroshevi Bublichenko, 1974 



1974 Isopoma nekhoroshevi Bublichenko: 73, text-fig. 9; pi. 2, 

 fig. 9. 



Comment. This species is from the Emsian of the Rudnogo Altai, 

 Ural Mountains, Russia. The specimens are small, the ventral sulcus 

 starts near the ventral umbo and ribbing is confined anteriorly, 

 associated with the fold and sulcus. The hinge plate appears to be 

 divided (Bublichenko, 1974: text-fig. 9) and the lack of a median 

 septum is normal for the genus. 



Isopoma orthoglossa (Torley, 1908) 



Fig 15 



1 908 Camarophoria orthoglossa Torley: 29, pi. 3, figs 20, 2 1 , pi. 



4, figs 1-3. 

 1 95 1 Isopoma orthoglossa (Torley); Schmidt: 87, pi. 1 , figs 6a-d. 



Comment. Schmidt (1951) redescribed this species from the 

 Flinzkalk (Upper Givetian) in the IserlohnT^etmathe area on the east 

 side of the river Rhine, Germany. The lectoty pe (Schmidt, 1 95 1 : pi . 

 1, fig. 6) is comparable to the wide Givetian specimens of Isopoma 

 brachyptyctum. No information on internal structures was given by 

 Schmidt. Further work on this species and the wider form of /. 

 brachyptyctum from the Upper Givetian of the eastern Rhine area is 

 needed to establish their relationships. We have studied two speci- 

 mens from Bilveringsen (SMF XVII 478a), but have not been able to 

 prepare sections. 



Isopoma ovale Xian Si-yan & Jiang Zong-long, 1978 



1978 Isopoma ovale Xian & Jiang: 289, pi. 106, fig. 13. 



Comment. Isopoma ovale is from the lower part of the Dushan 

 Formation (Givetian), Dongyao, Xiasi, Dushan County, Guizhou, 

 China. Externally this species somewhat resembles the wider forms 

 of/, brachyptyctum found in the Upper Givetian strata of Germany. 

 Xian & Jiang (1978: 289) record 'dental plates fused with the wall of 

 shell'. However, we have seen no evidence of dental plates as 

 compared to simple shell wall thickening. They also report that 

 crural plates and hinge plates are separated and the cardinal process 

 absent. /. ovale differs from the type species in being wider in 

 outline, having a weak sulcus and 7 to 8 anterior ribs close to the 

 commissure. 



Fig. 16 Isopoma? ren Schmidt. Holotype, dorsal, ventral, anterior (x2) 

 and lateral views; Flinzkalk, Schleddenhof bei Iserlohn; SMF XVII 

 1163a, x 1.7 (from Schmidt, 1951: pi. 1). 



Isopoma? ren Schmidt, 1951 



Fig. 16 



71908 Camarophoria aptycta (Schnur); Torley: 30, pi. 6, figs 4, 5. 

 1951 Isopoma? ren Schmidt: 88, pi. 1 , fig. 4. 



Comment. Schmidt assigned her species doubtfully to Isopoma; 

 it is from the Upper Givetian Flinzkalk in the Iserlohn-Letmathe 

 area, Germany. The figured specimen (Schmidt, 1951: pi. 1, fig. 4) 

 appears to be somewhat wider than /. brachyptyctum. deeper bodied 

 and has indistinct ribs. Schmidt described a divided hinge plate, 

 weakly curved and ventrally directed crura, and the absence of an 

 internal median septum, all features that are consistent withlsopoma. 

 We have seen two specimens from Schleddenhof (SMF XVII 1 163b, 

 1 163c). but have not been able to prepare sections for internal study. 



Fig. 17 Isopoma xestum Torley. Dorsal, ventral, anterior and lateral 

 views; Givetian, Massenkalk, Bilveringsen, Germany; BD 12785, x 3. 



Fig. 18 Isopoma xestum Torley. Sections through the specimen from 

 Massenkalk, Germany, figured in Fig. 17, x 9. 



