conchifera. 



Family XY.— Mactrid-e,* 



Includes Vattganella (p. 479), Lutraiiia (p. 479), Mactea 

 (p. 477), GxATHODON- (p. 478), Heterocordia, Anatinella 

 (p. 479), Cardllia (p. 469), and 



PsETJDOCARDniM, Gabb. 



Type, Cardium Gabbi, Kemond. Miocene and Pliocene. 

 California. 



Etymology, pseudo, false, and cardium. a generic name. 



Shell thick, heavy, resembling Lcevicardium externally ; liga- 

 ment internal ; lunnle cordate ; left yalye with a large carti- 

 lage pit and a Y-shaped tooth, which articulates in a cor- 

 responding depression in the right valve ; 2 lateral teeth in 

 each valve, very strong and prominent. 



Family XYIII. — MYAcrD^.f 

 POEOMYA, Forbes, 1843 (see p. 491). 



Passing into the genus Mya. 



Example, P. granulata. 



Synonyms, Eucharis, Eecluz; Embla, Loven; Cumingia 

 parthenopoea, Tiberri {non Thetis, Sby.). 



Animal with unequal siphons, clothed with numerous fila- 

 ments, foot narrow and slender. 



Shell sub-orbicular, sub-equivalve, and inequilateral, thin, 

 transparent, slightly nacreous within; valves closed, surface 

 granulated ; teeth, in right valve, a short but strong cardinal, 

 and in the left a minute triangular cardinal and a ridge -like 

 j^teral on the posterior side. 



Distribution, 10 species. Britain, Scandinavia, Mediten'anean, 

 Tropical America. 



Fossil, 13 species. Eocene. France, Germany, England, 

 United States. 



CoRBULOMYA, Nyst, 1846 (see p. 490). 



Derivation, Corhula and Mya. 



Examples, Corbula complanata, Sowerby ; Lentidium Medi- 

 terraneum, Jan and Cristofori. 



Shell oval, transverse, depressed, closed, inequivalve, sub- 

 inequilateral ; right valve the larger, with one pyramidal tooth, 



» See p. 477. • t See p. 489. 



