cardiidjE. 453 



other valve ; front lateral tooth none, hinder rudimentary. 

 Siphonal inflection none. 



Sijn. Cyrenella, Desk. Cyrenoides, Sow. Cyrenodonta, 

 Auct. 



Ex. C. Dupontia, Joannis, pi. Ill, fig. 5. Shell, C. 

 Dupontia, fig. 5, a, 5, b. 



The typical species of Cyrenoida is from the rivers of 

 Senegal. The mantle is simple-edged, and is open in 

 front and helow; the siphons are united and short; the 

 gills are unequal, narrow, and united behind ; and the foot 

 is cylindrical and elongated. 



Species of Cyrenoida. 



Dupontia, Joannis. Senegalensis, Dcsh. 



lenticularis, Desh. 



Fam. CARDIID^E. 



Palpi slender, acuminate. Mantle freely open in front ; 

 siphons distinct, but very short, and nearly sessile, their 

 bases and sides furnished with tentacular filaments ; gills 

 two on each side, thick, united together behind the body. 

 Foot very long and geniculate. 



Shell regular, equivalve, more or less cordiform, usually 

 inflated, closed or gaping posteriorly ; epidermis thin, 

 rarely distinct ; surface of valves usually radiately ribbed 

 or furrowed, rarely smooth ; margins crenulated. Hinge 

 composed of two oblique primary teeth in each valve, and 

 two elongate, lamellar laterals ; ligament external, short, 

 conspicuous. Muscular impressions sub-quadrate ; pallial 

 line simple, or slightly sinuated behind. 



VOL. II. 3 N 



