150 ANATINID^. 



Diatr. — 31 sp. India, Philippines, New Zealand, Japan, 

 United States. Fossil, 50 sp, Devonian? — Oolite — ; United 

 States, Europe. A. truncata^ Lam. (cviii, 71). 



Shell oblojig, ventricose, subequi valve, thin and translucent, 

 posterior side attenuated andg'aping; umbones fissured, directed 

 backwards, supported internally by an oblique plate ; hinge 

 with a spoon-shaped cartilage-process in each valve, furnished 

 in front with a tran verse ossicle ; pallial sinus wide and shallow. 



Animal with a closed mantle and long united sijahons, clothed 

 with wrinkled epidermis ; gills one on each side, thick, deeply 

 plaited; palpi very long and narrow; pedal opening minute, 

 foot very small, compressed. 



PLATYMYA, Agassiz, 1838. Some of the species of this fossil 

 group are more compressed than the recent Anatinae, but it can 

 scarcely be considered generically distinct. A. rostrata, Agass. 



CERCOMYA, Agassiz, 1842. Shell elongated, compressed; beaks 

 fissured; posterior slope frequentW angulated. Jurassic, Creta- 

 ceous. A. gracilis^ of Australia, is a recent species. A. striata, 

 Agassiz (cviii, 12). Jurassic. 



PLECTOMYA, Loriol, 1868. Shell ovately elongated, equivalve, 

 beaks subcentral, a strong oblique rib posterior to them; hinge 

 edentulous ; ligament external. Based on a well-known Jurassic 

 fossil, the Tellina rugosa of Komer. Appears to be scarcely 

 distinguishable, however, from Platymya. 



PERiPLOMYA, Conrad, 1870. (Leptomya, Conrad [not A. 

 Adams], 1867. Plicomya, Stoliczka, 1870.) Shell oblong, perla- 

 ceous, gaping anteriorly ; hinge with a spoon-shaped cartilage- 

 pi'ocess, forming an oblique callosity, which extends to the car- 

 dinal margin ; an obsolete rib and fissure run obliquely from the 

 anterior side of the beak. The genus is evidently closely allied 

 to Anatina, from which it chiefly differs b}^ the rib and fissure 

 anterior to the beak. Based on a North American cretaceous 

 species. P. applicata, Conrad. 



ANATiMYA, Courad, 1860. Shell oblong, like an Anatina, ante- 

 rior side with concentric sulci, posterior with radiating ribs. 

 Only American and cretaceous. A. anteradiata, Conr. (cviii, 73). 



Anthracomya, Salter, 1861. 



Etym. — Anthrax, coal, and mya, a generic name. 



Syn. — Naiadites, Dawson. 



Distr. — 9 sp. Coal-measures, associated with marine animals. 

 Great Britain, Nova Scotia. A. Adamsi, Salter. 



Shell thin, equivalve, the right valve rather larger ; valves 

 close, oblong, wider behind, where there is a blunt siphonal 

 ridge ; rounded anteriorly, with a byssal sinus on the anterior 

 ventral edge. Beaks small, anterior, and slightly prominent, 



