446 



MOLLUSCA 



PHYLUM VI 



Family 18. Pinnidae Meek. 



Shell mytiliform, not alate, dimyarian, the anterior adductor smaller ; equivalve, 

 truncate and wholly open behind; edentulotis ; area linear; ligament imrivincular, 

 internal ; shell structure coarsely frismatic, with a thin, partial, nacreous lining ; 

 byssiferous. Devonian to Recent. 



Palaeopinna Hall. Devonian ; North America. 



Aviculopinna Meek. A very small wing in front of the beaks. Carboniferoiis 

 and Permian. 



Pinna Linn. (Fig. 669). Shell thin, with a long hinge line and emarginate 

 nacreous layer ; valves carinate, the carina sulcate, section triangular. Jura to 

 Recent. 



Pinnigena Sauss. {Trichites Plott) (Fig. 670). Muscular impression very large; 

 prismatic layer extremely thick ; sculpture divaricate. Jura and Cretaceous. 



Atrina Gray. Shell with broad adductor scars ; short hinge line, no sulcus or 

 carina, the nacreous layer entire. Carboniferous to Recent. 



Cyrtopinna Morch. Jura to Recent. 



Family 19. Conocardiidae Neumayr. 



Shell sub-trigonal, anteriorly truncate and gaping, the margins of the gape frequently 



produced into a tube-like rostrum and sharply serrate below, the posterior end usually 



alate, the wing divided internally by a longitudinal ridge; 



dimyarian, the anterior adductor scars smaller ; equivalve 



more or less gaping behind ; schizodont, with a single 



anterior lateral, and an obscure or obsolete cardinal 



tubercle ; area ill-defined, amphidetic ; ligament external, 



parivincular ; shell structure cancellate, or btdlt up of 



holloio prisms resembling those of Pinna, but not solid ; 



valves thick, internally marginate ; byssifeous (?) ; marine. 



Conocardium alaeforme Sowerby. Ordovician to Carboniferous. 

 Lower Carboniferous ; Tournay, Bel- 

 gium, i/i. This group includes Conocardium Bronn [Pleurorhynchiis 



Phill.) (Fig. 671), and lihipidocanlium Fischer. It is ex- 

 tremely isolated, and comprises some fifty species. These remarkable shells have been 

 referred by most paleontologists to tlie Cardiacea, with wliich they have no connection what- 

 ever except analogy of form with a few aberrant Cardiidae. 



Fl(i. 071. 



Family 20. Pernidae Zittel. 

 Shell sub-mytiliform, with a broad posterior wing ; monomyarian, the anterior adductor 



Fir.. 672. 

 A, Gervillia aviculoiden Sow. Oxfordian ; Dives, Calvados. li, G. /mea/i.s- Bouvijjiiier. 



Hinfre. 



absent in the adult ; inequivalve, teeth irregular or absent, with a serial muUivincular 

 ligament ; byssiferous, with a moderate gape, or none. Permian to Recent. 



