PANAMIC-PACIFIC PELECYPODA 259 



an escutcheon Is usually well developed although wanting in some 

 cases. The surface is seldom completely smooth, more often heavily 

 sculptured with concentric lamellae, radial ribs or both. Ventral mar- 

 gins cremdated. 



Subfamily Venerinae 



VI. Shell usually small, smooth or with concentric sculpture, color often 

 purple. The species are ovoviviparous and carry the young within the 

 perivisceral cavity for a considerable time. This subfamily includes 

 several small venerids referred to the genera. Gemma, Parastarte, and 

 Psephidia. Species locally common. 



Subfamily Gemminae 



Subfamily DOSOILNAE H. and A. Adams, 1858 



Shell orbicular, equivalve, slightly or strongly convex, white and con- 

 centrically sculptured. Hinge plate wide, bearing three cardinal teeth in 

 each valve, and in some groups, a small anterior lateral tooth is present in 

 the left valve. Pallial sinus large, the ventral margins smooth. 



Two genera are present in the Panamic-Pacific region. 



I. The left valve has a small anterior lateral tooth and a corresponding 

 socket or pit in the right valve. Sculpture produced by rather strong, 

 ribbon-like, concentric bands. Lunule deeply impressed. 



Genus Dosinia 



II. No lateral teeth. The surface sculpture is finer, produced by closely 

 spaced, threadlike, concentric growth lines. The lunule is weakly de^ 

 fined, not impressed. 



Genus Cyclinella 



Genus DOSINIA Scopoli, 1777 

 Type species by tautonymy and monotypy, Chama dosina Adanson 

 {•=Dosinia africana Hanley). 



Shell subcircular to suborbicular, depressed or convex, white, the sur- 

 face finely sculptured with incised concentric lines, evenly spaced and 

 forming ribbon-like bands, narrow or quite wide. Lunule small and deeply 

 depressed; the escutcheon absent in American species. The hinge plate high, 

 mostly posterior of the cardinal teeth with a wide scar above for the liga- 

 ment attachment, usually deeply inset and overhung by the margin of 

 the shell. Hinge with three cardinal teeth in each valve, the left middle 

 tooth and the right, posterior tooth large and bifid. There is a small, anterior 

 lateral tooth in the left valve but merely a small socket or pit for its re- 

 ception in the right valve. The adductor scars are large and subequal in 

 size, connected across by the pallial line bearing a deep, V-shaped sinus. 

 The ventral margins are smooth. Periostracum thin, gray, or straw-colored. 



Subgenus DOSmiDIA Ball, 1902 

 Type species by original designation, Dosinia concentrica Born. Recent, 

 West Indies, and the eastern seaboard of the United States northward to 

 Hatteras. 



No escutcheon. Members of this subgenus are confined to the warm 

 temperate and tropical waters of America where it replaces all other sec- 

 tions of the genus. 



