374 MOLLUSCA SUB-KINGDOM VI 
Terquemia, Tate (Carpenteria, Desl.) Shell with a marginal ridge, sessile by the 
right valve; left valve flatter, free. Trias and Lias. 

Fic. 641. Fic. 642. 
Exogyra columba, Lam. Greensand (Ceno- Exogyra flabellata, Goldf. sp. Cenomanian; Saint Paul 
manian); Regensburg, Bavaria. Cloister, Egypt. 
Family 25. Eligmidae. Guill. 
Shell thick, sub-equivalve, free when adult, resembling Chalmasia in form, anteriorly 
with an trreqular pedal gape ; edentulous, monomyarian, with the adductor seated on the 
free extremity of a myophore projecting from the wmbonal 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, with 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 ; byssus obsolete ; young usually with a distinct nepionie 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, Dawson; Asthenodonta, Whiteaves ; Carbonicola, 
M‘Coy. Coal Measures. Palaeomutela and Oligodon, Amalitzky. Brackish Permian 
marls of Russia. 
