TRIBE ARCACEA. 169 



with a smooth dorsal area reaching thence to the anterior ex- 

 tremity. — Enrjland. 



N. Parva. Sow. in Condi. III. f. 7. — Reeve, t. 85. f. 7. 

 Oblong, white, thickish, with an oUvaceous epidermis, transversely 

 grooved ; posterior side rounded, anterior rather beaked, angular : 

 dorsal area anteriorly not grooved. -^^ . . h' — N. Pole. 



N. PoLiTA. Sow. Z. P. 1832.— C"/./. II.— Reeve, t. S^i. 

 y. 1 1 . Oblong anteriorly beaked, white under a polished greenish 

 epidermis, anterior dorsal edge, smooth ; with some oblique an- 

 terior striae, ^^q . . l-f*j. — Panama. 



N. CosTELLATA. Sow. Z. P. 1832.— CoH. II. f. 238.— 

 Reeve, t. 85. f. 8. Oblong, thin, covered with small concentric 

 acute riblets ; anteriorly beaked and acuminated, with two dorsal 

 approximated and crenulated ribs. 4 . . 4. — Panama. 



N. GiBBosA. Sow. Z. P. \So2.— Reeve, t. 85. /. 9. — Con. 

 II. f. 9. Oblong, gibbous, anteriorly acuminated and beaked, 

 transversely grooved ; anterior dorsal edge depressed, with the 

 central margin elevated. ^ . . \^.- — Peru. 



N. Elenensis. Sow. Z. P. IS32.— Reeve, t. 85. /. \A.—Con. 

 II. f. 14. Ovate, gibbous, transversely grooved, anteriorly acumi- 

 nated and beaked ; anterior dorsal margin arcuated, the margins 

 crenulated. t7o • • i- — ^^- Colombia. 



N. Eburnea. Sow. Z. P. i832. Ovate gibbous, transversely 

 grooved, glossy, ivory-like, anteriorly acuminated and beaked. 

 ■Jo..-i;f.— IF. Colombia. 



N. CuNEATA. Sow. Z. p. \S32. — Reeve, t. 85. /. 15. — Con. 

 II. f. 15. Ovate, wedge-shaped, gibbous, concentrically grooved, 

 the epidermis greenish, glossy, the posterior side rounded the 

 anterior acuminated. ^ . . |. — Valparaiso. 



N. Throc^formis. Storer. Host. J. of N. H. 2. — Gould. 

 Mas. f. Q&. Large, oblong ovate, gaping at both ends, posteriorly 

 rounded and shorter, anteriorly broader and obliquely subtruncated 

 so that the dorsal extends further than the ventral edge ; a rib-like 

 wave passes from the beaks to the ventral anterior angle : cuticle 

 dark olive green : hinge with a very large spoon shaped tooth on each 

 side of which are twelve teeth, each one folded from the centre to 

 an angle of forty-five degrees : inside polished white. H§ • • 2|. — 

 North America. 



N. EiGHTSii. Couthouy Annals Lyceum, N. H. — Say. Cat. 

 t. i. f. 12, 3. Subelliptical, glossy, convex, moderately thick, sub- 

 equilateral, posterior side rather longer ; anterior side very slightly 

 and obtusely rostrated ; ventral edge entire, much arcuated ; dorsal 

 edges but little sloping, the anterior subincurved, the posterior con- 

 vex : cuticle blackish ohve, marked only by the prominent lines of 

 growth ; no anterior depression : inside dull bluish white ; hinge 

 broad, teeth few and obtuse, cardinal pit triangular, i . . 1 1 . — In 



