MARINE MOLLUSCA OF THE UNITED STATES. 141 
Genus CORBULA, 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. 326, 327. 
Journ. Philad. Acad., ii. 812. 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 their 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. 
New England to Florida. 
Genus NEEZRA, Gray. 
- Griffith’s Cuvier. 18384. 
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. peniucipa, Stimpson. Fig. 328. 
Invert. Grand Manan., 21, fig. 18. 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 strie 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 34, diam. 3 mill. 
New England, northwards. 
