466 



MOLLUSGA 



PHYIAIM VI 



valve, (japing, edentulous, or with an obscure subumhonal tubercle; ligament, and 

 resilium external, opisthodetic, seated on nymphae ; area obsolete or obscure, not amphi- 

 detic ; beaks entire ; pallial sinus loell viarked ; marine. Trias to Recent. 



Pholadomya Sow. (Figs. 739-741). Sliell thin, sub-ovate, with radial and con- 

 centric sculpture, inflated, and with rather prominent beaks ; hinge edentulous, or 

 with an ol)scure thickening ; scars feeble, pallial sinus moderately deep. In the 



Gonimnya duboisi Ag. Inferior Oolite ; Bayeux, 

 Calvados. A, Shell, l/j. B, Surface showing puncta- 

 tions, magnified. 



Fig. 743. 



Ilinnomyd (Arcomya) calreifortiii.i Ag. Inferior Oolite ; 

 Les Moutieux, near Bayeux, Calvados, -/s. 



posterior dorsal region the radial sculptui'e is usually feeble or absent. Lower Lias to 

 Recent ; formerly very abundant, but now represented by a single species from the 

 Antilles, P. Candida Ag., and another from Japan. 



Procardia Meek. Includes those forms with an escutcheon. Jura. 



Goniomya Ag. (Fig. 742). With V-shaped sculpture. Lias to Cretaceous ; very 

 plentiful in Middle and UiJper Jura. 



Homomya Ag. {Arcomya, Myopsis Ag. p.p.) (Fig. 743). Distinguished from the 

 typical Pholadomyas by its smooth or very finely sculptured shell, without rilts. 

 Trias to Cretaceous. 



(?) Machomya, Plectomya Loriol ; Mactromya Ag. Jura and Cretaceous. 



Family 4. Anatinidae Dall. 



Soft pchHs like Pholadomya, the foot small and grooved, ventral foramina small, and 

 the siphons with a horny integument, not entirely retractile. Shell sub-equivalve, truncate, 



or gaping behind, edentulous, the resilium internal between 

 two spoon-like chondrophores vertically directed and often 

 supported by buttresses ; ligament obsolete or absent ; area 

 obsolete; beaks transversely fissured; pallial sinus well 

 marked ; monoecious ; marine. Jura to Recent. 



Anatina Lam. (Plafymya, Ccrcomya Ag.; Plicomya 

 Stol.) (Fig. 744). Shell thin, nearly equivalve, con- 

 centrically but feebly sculptured, posterior side shorter 

 than the anterior. Jura to Recent. Laternula Bolten, is a prior name. 

 Periplomya and Anatimya Conrad ; Rhynchomya Agassiz. Cretaceous. 



Fig. 744. 



Anatina prmhicta Zittel. Upper 

 Cretaceous ; Gosau Valley, Austria. 



Family 5. Periplomatida,e Dall. 



Shell sub-nacreous, conspicuously inequivalve, nearly closed, edentulous; the resilium 

 internal, between two anteriorly or vertically directed chondrophores, often buttressed, the 

 lithodesma rarely wanting ; ligament and area, absent ; beaks fissured ; pallial sinus 

 broad and shallow; siphons separated to their bases, naked and ivholly retractile; mono- 

 ecious; marine. Tertiary and Recent. 



