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. J_. _ ^ ^_ — Enfjland, ^'' 

 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. f . . i^. — 

 China. 



N. PisuM. Sow. Z. P. \S32.—Sow. Con. II. f. 23. Small 

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

 inclined. ^ . . \. — Valparaiso. 



N. ExiGUA. Sow. Z. P. 1832.— Cow. II. f. 24. SmaD, 

 obliquely ovate, whitish pellucid, concentrically grooved ; anterior 

 side the longer, subacuminated, the posterior extremely short. 

 ^\ . . -1. — 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 strise, posterior 

 margin very short and very obtusely rounded, a submarginal im- 

 pressed line ; antei'ior 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 rnore 

 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 t7-ans- 

 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. Pectinata. Lam. — T. Margaritacea. An. du. Mus. t. 

 67. f 2.— Sow. G. f. 1, 2.—BI. t. 70. /. \.— Peeve, 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. 



