172 TESTACEOUS MOLLUSCA. 
parallel to the but slightly arcuated and entire ventral, forming an 
angle at its extremity and by a broadly rounded curve, united to 
the ventral (the tip is therefore not angular but very obtuse); 
beaks prominent, recurved, having a deep pit before them; pos- 
terior side extremely short; teeth very long and slender, about 
eight anterior and four or five posterior. =3,. .+.—ngland, 5° 
North America. 
N. Convexa. Sow. Conch. Il. f. 22. Ovate, turgid, whitish 
smooth, posterior side the shorter, slightly acuminated ; anterior 
side much longer: dorsal slope rounded; ventral margin entire ; 
hinge pit very oblique, teeth of posterior side very few. ~2..$).-— 
China. 
N. Pisum. Sow. Z. P. 1832.—Sow. Con. Il. f. 23. Small 
obliquely oval, the posterior side very short, the dorsal margin 
inclined. 1..3.—Valparaiso. 
N. Exigua. Sow. Z. P. 1832.—Con. Il. f. 24. Small, 
obliquely ovate, whitish pellucid, concentrically grooved ; anterior 
side the longer, subacuminated, the posterior extremely short. 
3 --4-—W. Colombia. 
N. Proxima. Say. Jour. A. N. S. Phil. 2. p. 270.— 
Gould. Mas. p. 104. Subtriangular, oblique, concentrically 
wrinkled, with numerous minute longitudinal strie, posterior 
margin very short and very obtusely rounded, a submarginal im- 
pressed line; anterior margin very oblique, and but slightly arcu- 
ated: umbo placed far back: inner edge strongly crenated ; teeth 
stout, posterior row very distinct and regular. j.—U. States. 
Very like Nucleus but wider, and the posterior row of teeth more 
reqular. 
TRIBE TRIGONIACEA. 
Primary, lamelliform and transversely striated teeth . 
TRIGONIA. 
Equivalve, inequilateral, trigonal, and sometimes orbicular ; teeth 
of the hinge oblong, laterally compressed, diverging, with trans- 
verse furrows ; two in the right valve grooved on both sides ; 
and four in the left valve, grooved on one side; ligament mar- 
ginal and external. 
T. Pecrinata. Lam.—T. Marearitracea. An. du. Mus. t. 
67. f. 2.— Sow. G. f. 1, 2.—Bl. t. 70. f. 1.—Reeve. t. 86.— 
Cuama P. W.S.t. 2. f. 6. Suborbicular, longer than broad, with 
radiating roughish verrucose and elevated ribs ; margin plaited. 
1.—New Holland. 
