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. -fy . . %. — England, fy 

 North America. 



N. Convexa. Sow. Conch. II. 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. J- . . -J-J. — 

 China. 



N. Pisum. Sow. Z. P. 1832.— Sow. Con. II. f. 23. Small 

 obliquely oval, the posterior side very short, the dorsal margin 

 inclined. J . . \. — Valparaiso. 



N. Exigua. Sow. Z. P. 1832.— Cow. II. /. 24. Small, 

 obliquely ovate, whitish pellucid, concentrically grooved ; anterior 

 side the longer, subacuminated, the posterior extremely short. 

 ■fa . . ^. — W. Colombia. 



' N. Proxima. Say. Jour. A. N. S. Phil. 2. p. 270.— 

 Gould. Mas. p. 104. Sub triangular, oblique, concentrically 

 wrinkled, with numerous minute longitudinal striae, 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. ^V — ^ ^ a ^ es ' 

 Very like Nucleus but wider, and the posterior row of teeth more 

 regular. 



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 rigid valve grooved on both sides ; 

 and four in the left valve, grooved on one side ; ligament mar- 

 ginal and external. 



T. Pectin ata. Lam. — T. Margaritacea. An. du. Mus. t. 

 67. f 2.— Sow. G.f. I, 2.—BL t. 70. f. 1.-— Reeve, t. 86.— 

 Cham a P. W. S. t. 2.f. 6. Suborbicular, longer than broad, with 

 radiating roughish verrucose and elevated ribs ; margin plaited. 

 1 . — New Holland. 



