264: TESTACEOUS MOLLUSCA. 



come obsolete as they approach the but slightly rounded anterior 

 ventral edge : horn coloured, more or less dark, the wrinkles of 

 growtli which run nearly at right angles, from the straight dorsal 

 edge, very conspicuous at the ventral edge (near which the ribscea&e) 

 this latter which is about equal to the dorsal is incurved near the 

 beaks and thence proceeds in nearly a straight outward direction to 

 the broad open extremity. 10. — Britain. The ribs are further 

 apart and less numerous than in Pectinata. 



P. Vexillum. Born. t. 7. /. 8.—Gmel. 3365.— D. p. 329.— 

 Lam. 14.— Ch.f. 783.— W. t. 13. f. 11. Short, broad, brown 

 with blackish clouds, retuse at the anterior ventral margin, the ven- 

 tral edge in receding from the beaks, much dilated and transversely 

 wrinkled ; the disk anteriorly with longitudinal unarmed ribs. 5. 

 East Indies. Not unlike the next but is smaller and the anterior 

 ventral margin broader in proportion and less rounded, the sides are 

 more abruptly curved. 



P. Nigra. Ch.f. 774.— D. p. 325.— Sow. G.— Reeve, t. 104.— 

 W. t, 12. f 2.— P. Nigrina. Lam.5.—E. t. 199./. 1. Ovate, 

 ventricose, with the margin rounded on both sides, opaque, blackish 

 within and without, with some radiating striae, which are most ap- 

 parent at the beaks, usually with a few distant vaulted scales towards 

 the anterior ventral margin. 10. — Indian & Ocean. 



P. Serrata. Sow. G, — Reeve, t. 103. — Desh in Lam. vol. 7 . p. 

 07. Elongated, triangular, thin, pellucid, yellowish horn coloured, 

 both the sides straight and forming an acute angle at the beaks, the 

 posterior one obtuse and obliquely rounded : the surface divided 

 into two portions, the anterior one with longitudinal diverging sulci 

 armed with imbricated scales even to the margin which thus re- 

 sembles the edge of a saw, the other with curved lines of growth 

 surmounted by small rather depressed scales. 5. — New South 

 Wales. 



P. Adusta. Chemnitz, f. 782.— D. p. 328* — P. Exusta. Gmel. 

 3366. — W. 1. 13. f. 10. Subtriangular-ovate, rather short, transverse- 

 ly wrinkled, with several smooth and a few broad spinous ribs : 

 brownish horn-coloured, with dusky rays ; posterior ventral much 

 arcuated ; dorsal edge subincurved, nearly straight, anterior base 

 slightly arcuated, broad, rounded at the sides. 5. Manilla. Not 

 unlike Seminuda but the dorsal edge is shorter, less straight and more 

 rounded at the end. 



P. Incurva. Gmel 3366.— D. p. 330.— Ch. f. 778.— E. t. r 200. 

 f. 3. — W.t. 13. f. 15. Very narrow, triangular, dorsal edge the 

 longer, incurved ; posterior ventral nearly straight, keeled in the 

 middle of the shell, transversely wrinkled, fulvous, with a few 

 radiating stria;: anterior base arcuated: apex very acute. 11. 

 Nicobar Isles. 



P. Papyracua. Chem.f. 786.— Gmel. 3367.— D, p. 331.— W. 



