CLASS I 



PELECYPODA 



451 



Terquemia Tate {Garpenteria Desl.). Shell with a marginal ridge, sessile by the 



right valve 



left valve flatter, free. Trias and Lias. 



Fig. 690. 



Exogyra columha Lam. Greensand (Ceno- 

 manian) ; Regensbnrg, Bavaria. 



Pio. 691. 



Exngym fiahcUatoi (Goldfuss). Cenonianian 

 Saint Pan! Cloister, Egypt. 



Family 25. Eligmidae Gill. 



Shell thick, suh-equivalve, free when adult, resembling Chalnuma in form,, anteriorly 

 with an irregular pedal gape ; edentulous, monomyarian, ivith 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 

 desiraljle. 



Further investigation of the genus is 



Superfamily 5. NAIADACEA Menke. 



Shell of varied form, normally equivalve 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 nepionic stage ; station 

 usually fiuviatile or lacustrine. 



Family 26. Oardiniidae Zittel. 



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

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

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



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



Garbonicola M'Coy {Anthracosia King) (Fig. 692). Shell thin, oblong ; hinge 

 with a blunt elongated cardinal, and a feeble posterior lateral tooth upon a thickened 

 hinge plate. Common in the Coar Measures and estuarine Permian of Russia, also 

 America and Africa. 



Naiadites Dawson {Anthracoftera Salter). Shell modioliform, obliquely triangular, 

 with almost terminal beaks, straight hinge-line, striated hinge-plate, and superficially 

 marked with flat concentric lamellae. Coal Measures ; North America and Europe. 



