MARINE MOLLUSCA OP THE UNITED STATES. 141 



Genus COBBITLA, Bruguiere. 

 Encyc, Meth., t. 230. 1792. 



Animal with very short, united siphons; orifices fringed; foot 

 thick and pointed ; palpi moderate ; gills, two on each side, ob- 

 scurely striated. 



An extensive genus, of universal distribution. 



1. C. coNTRACTA, Say. Figs. 32G, 327. 

 Journ. Philad. Acad., ii. 312. 1822. 



Shell small, solid, convex ; valves subequal, shortest and 

 rounded in front, long and pointed behind. Beaks rather promi- 

 nent, nearly touching each other at tlieir points ; basal margin 

 contracted and concave in the middle. Surface with regular equi- 

 distant concentric impressed lines and intervening ridges. A 

 prominent ridge runs from the beaks on each side to the posterior 

 basal margin, including a broad space between them ; left valve 

 shutting within the other along the basal margin. Epidermis thin. 

 In one valve the tooth is simple, hooked and turned towards the 

 beak ; in the other, it is broader than high, projecting at right 

 angles to the valve, with a deep cavity on the posterior side of the 

 base for the reception of the hooked tooth. Epidermis dull brown. 



Length 10, height 6.25, diam. 5 mill. 



Neio England to Florida. 



Genus NEJERA, Gray. 

 Griffith's Cuvier. 1834. 



Animal with closed mantle, lanceolate foot and short, united 

 siphons, branchial one largest, the anal with a membranous valve, 

 both with a few long, lateral cirri. A genus of quite small shells, 

 universally distributed. About twenty-five species are described. 



1. N. PELLUCiDA, Stimpson. Fig. 328. 



Invert. Graud Manan., 21, fig. 13. 1853. 



Shell small, thin, pale white, subovate, swollen anteriorly, and 

 contracted posteriorly into a short but distinct rostrum. Beaks 

 small, tumid, and placed a little before the middle. Surface nearly 

 smooth about the beaks, with irregular, distant striae of growth 

 near the margin, which become sharp and well marked on the ros- 

 trum. Within smooth and glossy, with minute radiating lines 

 across the disk; teeth very minute. Epidermis white, sometimes 

 pale greenish on the beaks and brownish on the rostrum. 



Length 5, height 3-f , diam. 3 mill. 



New /England^ northwards. 



