254 TESTACEOUS MOLLUSCA. 
come obsolete as they approach the but slightly rounded anterior 
ventral edge: horn coloured, more or less dark, the wrinkles of 
growth which run nearly at right angles, from the straight dorsal 
edge, very conspicuous at the ventral edge (near which the ribs cease) 
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. Vexirtum. Born. t. 7. f. 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. Niagra. Ch. f. 774.—D. p. 325.—Sow. G.—Reeve. t. 104.— 
W. t, 12. f.2.—P. Niertna. Lam. 5.—E. t. 199. f. 1. Ovate, 
ventricose, with the margin rounded on both sides, opaque, blackish 
within and without, with some radiating striz, which are most ap- 
parent at the beaks, usually with a few distant vaulted scales towards 
the anterior ventral margin. 10.—Jndian Ocean. 
P. Serrata. Sow. G.—Reeve. t. 1038.—Desh in Lam. vol. 7. p. 
67. Elongated, triangular, thin, pellucid, yellowish horn coloured, 
both the sides straight and forming an acute angle at the beaks, the 
posterior one ebtuse 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. Apusta. Chemnitz. f. 782.—D. p. 328-— P. Exusta. Gmel. 
3366.—W.t.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. °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 striz: anterior base arcuated: apex very acute. 11. 
Nicobar Isles. 
P. Paryracsa. Chem. f. 786.—Gmel. 3367.—D. p. 331.—W, 
