374 



MOLLUSCA 



SUB-KINGDOM VI 



Terquemia, Tate (Carpentaria, Desl.) Shell with* a marginal ridge, sessile by the 

 right valve ; left valve flatter, free. Trias and Lias. 



FIG. 641. 

 Exogyra columba, Lam. Greensand (Ceno- 



manian); Regensburg, Bavaria. 



FIG. 642. 



Exogyra flctbellata, Golclf. sp. Cenomanian ; Saint Paul 

 Cloister, Egypt. 



Family 25. Eligmidae. Gill. 



Shell thick, sub-equivalve, free when adult, resembling Chalmasia in form, anteriorly 

 with an irregular pedal gape ; edentulous, monomyarian, with the adductor seated on the 

 free extremity of a myophore projecting from the umbonal cavity, otherwise like the 

 Ostreidae. Upper Jura. 



Eligmus, Desl. If the characters of this genus have been correctly interpreted, it 

 can hardly be retained in the Ostreidae. Further investigation of the genus is 

 desirable. 



Superfamily 5. NAIADACEA. Menke. 



Shell of varied form, normally equivalve, inequilateral, and dimyarian ; rarely 

 alate ; shell substance nacreous and prismatic, ivith a conspicuous epidermis; area 

 obscure or amphidetic ; ligament parivincular, usually opisthodetic and external ; pallial 

 lobes usually free, except for an anal siphon, the pallial line simple ; foot normally long, 

 compressed, keeled ; bijssus obsolete ; young usually with a distinct nepionic stage ; station 

 usually fluviatile or lacustrine. 



Family 26. Cardiniidae. Zittel. 



Shell equivalve, closed, with feeble concentric sculpture or smooth ; dentition Schizo- 

 dont or obscure; ligament opisthodetic, external; dimyarian, adductor scars sub-equal, 

 pedal scars feeble or invisible ; station marine or brackish water. Devonian to Trias. 



Amnigenia, Hall. Devonian (Catskill) of North America, and Rhenish Prussia. 



Anthracosia, King (Fig. 643). Shell thin, oblong ; hinge with a blunt elongated 

 cardinal, and a feeble posterior lateral tooth upon a thickened hinge plate. Common 

 in the Coal Measures and estuarine Permian of Russia. 



Anthracomya, Salter ; Nayadites, Dawsoii ; Asthenodonta, Whiteaves ; Carbonicola, 

 M'Coy. Coal Measures. Palaeomutela and Oligodon, Amalitzky. Brackish Permian 

 marls of Russia. 



