446 



MOLLUSCA 



PHYLUM VI 



Family 18. Pinnidae Meek. 



Shell mytüiform^ not alate, dimijarian, the anterior adductor smaller ; equivalve, 

 truncate and wholly open behind ; edentulous ; area linear ; ligament parivincular^ 

 internal ; shell structure coarsely prismatic, with a thin, partial, nacreous lininfj ; 



ferous. Devonian to Eecent. 



Palaeopinna Hall. Devonian ; North America. 



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

 and Permian. 



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

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

 Recent. • 



Pinnigena Sauss. (Trichites Plott) (Fig. 670). Muscular imj)ression 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. 



Gyrtopinna Mörch. Jura to Recent. 



Family 19. Oonocardiidae Neumayr. 



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

 produced into a tuhe-like rostrum and sharply serrate helow, the posterior end usually 



alate, the wing divided internally hy 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 built up of 

 hollow prisms resembling those of Pinna, but not solid ; 

 valves thick, internally marginate ; byssifeous {?) ; marine, 

 conocardium almforme Sowerby. Ordovician to Carboniferous. 



Lower Carboniferous ; Tournay, Bel- 



gium. i/i- This group inchides Conocardium Bronn {Pleurorhynchus 



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

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

 referred by most paleontologists to the Cardiacea, with which they liave no conncction what- 

 ever except analogy of form with a few aberrant Cardiidae. 



Family 20. Pernidae Zittel. 

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



Fig. 671. 



Fio. 672. 

 Ä, Gervülia aviculoides Sow. Oxfordian ; Dives, Calvados. B, G. linearis Bouvignier. Hinge. 



absent in the adult ; inequivalve, teeth irregulär or absent, with a serial multivincular 

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



