TRIBE ARCACEA. 171 



f. 62. Oblong, very smooth and shining, subequilateral, cuticle 

 light green occasionally with darker zones, and two or three lighter 

 radiations : anterior dorsal edge rectilinear nearly to the tip, which is 

 a little recurved pointed and not truncated : ventral edge scarcely 

 at all incurved : inside bluish white, subnacreous, twenty-two 

 posterior, eighteen anterior teeth, -f^ . . \-^^. — United States. 



* * * Elliptic. 



N. Margaritacea.* LaiJi. 6. — Philippi. j)- 64. t. 5. f. 8. 

 — Sow. G. f. 7. {good.)—kKCA M. Brug. Die. p. 109. — 

 Arca Nucleus. Lin. 1143. — D. p. 244. — Brooks. Intro. 

 t. 3. /. 36.— Z>a Cost. t. 15. / 6.—Petiv. t. 17. f. O.— Gualt. 

 t. 88. R. — W. t. 10. f. 42. Ovate subtriangular, moderately 

 convex, nearly smooth, some extremely fine radiating strise 

 being indistinctly visible near the crenated ventral edge ; cuticle 

 olive-yellow ; umbones prominent ; ventral edge rounded ; anterior 

 side much the longer, its dorsal edge moderately sloping ; posterior 

 edge all but direct (but not abrupt), convex : beaks acute and re- 

 curved : lunule defined by a shallow groove, inside pearly, hinge 

 with numerous straight sharp pectinated teeth. — A7i. Var ? (N. 

 PoLii ? Phil. p. 63. t. 5. y. 8.) Larger, more oblique and 

 triangular, olivaceous, with ridges of growth, posterior edge abrupt, 

 anterior more sloping. — England, France, ^'c. 



N. Decussata. Sow. Conch. II. f. 18. SomcAvhat tri- 

 angular, white, decussately striated ; posterior side shorter, its 

 slope rather elevated in the middle ; anterior side much longer, 

 oblique ; ventral margin rounded, its edge crenated. ^ . . ii. — 

 Guinea. 



N. RuGULOSA. Sow. Conch. II. f. 19. Ovate triangular, 

 with a greenish epidermis covered with rugulose striae ; angles 

 obtuse : posterior slope with a central elevation ; anterior slope 

 somewhat rounded ; ventral margin very finely crenulated. f • • i- 



N. NiTiDA.* Sow. Conch. II. f. 20. Ovate, subtriangular, 

 smooth, shining, white with an olive coloured epidermis : anterior 

 slope somewhat rounded, posterior nearly straight, with a central 

 elevation. ^ • •\- 



N. Obliqua. lam. 5. — Sow. Cone. II. f. 21. Obliquely 

 ovate, subelliptical, thin, pellucid, olive, smoothish ; posterior side 

 rounded, rather long in proportion to those of this division, its 

 edge convex : anterior side rounded, its dorsal edge much arcuated, 

 the margin very entire. ^ . . -|. — Valparaiso, South Seas. 



N. Tenuis.* Turt. B. p. \77.—F. p. 402.— Gould. Has. 



p. 105. /. 64 Arca T. llont. Sup. p. 56. t. 29. /. 1.— 



Pen. 4. p. 215.— i>. p. 246.— Turt. D. p. 11.— TF. t. 10. 

 _/. 45. Ovate-trapczoidal, thin, smooth, without radiating lines, 

 glossy grass green ; anterior dorsal line scarcely sloping, nearly 



