CONCHIFERA. 



Family XV.— Mactrilve,* 



Includes Vatjganella (p. 479), Ltjtraria (p. 479), Mactra 

 (p. 477), Gnathodon (p. 478), Heterocordia, Anatlnt:lla 

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



Pseudocardium, Gabb. 



Type, Cardium Gabbi, Eemond. Miocene and Pliocene. 

 California. 



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



Shell thick, heavy, resembling Lcevicardium externally ; liga- 

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

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

 responding depression in the right valve ; 2 lateral teeth in 

 each valve, very strong and prominent. 



Family XVIII. — MYAcro^.f 

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



Passing into the genus My a. 



Example, P. granulata. 



Synonyms, Eucharis, Kecluz; Embla, Loven; Cumingia 

 jparthenopoea, 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. 



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



Derivation, Corbula and My a. 



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. 



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