conchifera. 



Family XY. — Mactrid^,* 



Includes Vatjganella (p. 479), Ltjteahia (p. 479), Mactea 

 (p. 477), GrNATHODON (p. 478), Heterocordia, ANATHsTELLA 

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



Pseudocahdium, Gabb. 



Type, Cardium Gabbi, Eemond. Miocene and Pliocene. 

 California. 



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



Shell tbick, heavy, resembUng Lcevicardium externally ; liga- 

 ment internal ; lurnile cordate ; left valve with a large carti- 

 lage pit and a Y-sbaped 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 

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



Passing into the genus Mya. 



Example, P. granulata. 



Synonyms, Eucharis, Eecluz; Embla, Loven; Cumingia 

 ^arthenopoea, 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 

 lateral on the posterior side. 



Distribution, 10 species. Britain, Scandinavia, Mediterranean, 

 Tropical America. 



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

 United States. 



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



Derivation, Corhula and Mya. 



Examples, Corbula complanata, Sowe'rby ; 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. 



79 



