158 



M. MOHANTI AND C.H.C. BRUNTON 



Fig. 6 Isopoma gryps Schmidt. Sections through the socket region of a poorly preserved specimen showing thickened valves. Greifenstein Kalk. Lower 

 Eifelian, trench at Wiege, Greifenstein, Hessen, Germany; BD 12786. x 9. 



imiplication modified by a zig-zag commissure resulting from 6-7 

 short, anteriorly confined ribs . The ventral valve is further ornamented 

 by a median groove originating close to the umbo. 



Isopoma hertae has also been recorded by Ficner & Havlicek 

 (1978) from the Lower Givetian beds of the Celechovice area in 

 Moravia, Czech Republic. 



Isopoma isiliense Rzhonsnitskaya, 1953 



1953 Isopoma isiliensis Rzhonsnitskaya: 177, pi. 10, figs 12, 13. 



Comment. The only known occurrence is the original description 

 of specimens from the Upper Frasnian of the Kuznetsk Basin, 



7a 



7c 



Fig. 7 Isopoma hertae Mohanti. Dorsal, ventral, anterior and lateral 

 (anterior uppermost) views; Portilla Formation (Eifelian to Givetian) of 

 southern Cantabrica, Spain; BD12734, x 3. 



Figs 9, 10 Isopoma lummatoniensis (Davidson). 9a-d, Lectotype, here 

 selected (figured Davidson, 1865: pi. 14. fig. 14); dorsal, ventral, 

 anterior and lateral views with the umbo to the right; late Givetian, 

 Lummaton, Devon; BB 61841. x 3. lOa-d, dorsal, ventral, anterior and 

 lateral views (with the umbo to the left); late Givetian, Lummaton, 

 Devon; B 12802, x 3. 



Russia (Rzhonsnitskaya, 1953). The species is poorly characterized, 

 but appears to be rather small and deep bodied, with 3 ribs in the 

 ventral sulcus. Interiors are unknown. 



Isopoma lummatoniensis (Davidson, 1865) Figs 9-11,21 



1865 Rhynchonella lummatoniensis Davidson: 70, pi. 14, figs 

 14-17. 



Fig. 8 Isopoma hertae Mohanti. Portilla Formation (Eifelian to 

 Givetian). Cantabrica, Spain; sections of the specimen figured by 

 Mohanti (1972: figs 30.2, 30.3); specimen not registered. Geologisch en 

 Mineralogisch Instituut. Rijksuniversiteit, Leiden, x 8. 



Fig. 11 Isopoma lummatoniensis (Davidson). Sections through the socket 

 and hinge plate region. Lummaton Shell Bed, late Givetian, Lummaton, 

 Devon; BB 51959, x 9. 



