90 SYNOPSIS OF THE CHARACTERS OF THE 



This singular sliell is remarkable for the great size and regularity of the radiating ribs ; these are slightly 

 nodulous where they pass over the concentric ribs, which are about half their thickness ; the spaces resulting 

 from the crossing of these two sets of ribs are nearly square ; the ears are rather large and rectangular, wth 

 sharp, sigmoidal strise parallel with, the margin. Length three lines, width, three and a half lines. 



Pecten cingendus. M'Coy. (PL XVII. fig. 11). 



Sp. Ch. — Tnmcato-orblcular, slightly convex; ears unequal, posterior very large, rectangular, undefined; 

 anterior one small, narrow, smooth ; surface with about twelve concentric, angular, smooth ridges, becoming 

 obsolete on the large posterior eax. 



This strongly marked species at first sight bears a resemblance to the P. Sedgewickii, M'Coy, but It Is 

 smaller, less convex, and has much smaller and more numerous concentric ridges, the ears also are entirely 

 different. Length six lines, width seven lines. 



Pecten clathratus. M'Coy. (PL XIV. fig. 12). 



Sp. Ch. — Nearly orbicular, convex; surface with about fifteen strong, radiating ribs, between each pair of 

 which are three smaller ones, which are cancellated by transverse ribs equalling them in thickness. 



This beautiful shell has between each of the fifteen large ribs, three smaller ribs, the centre one of which 

 is slightly the largest ; it is these three smaller ribs only that are crossed by the transverse ridges ; those are 

 placed at such a distance, that the spaces resulting are nearly square : at each crossing of a longitudinal and 

 transverse rib, there is a swelling or tubercle produced. 



Pecten ccelatus. M'Coy. (PL XVIIL fig. 2). 



Sp.Ch — Shell convex, rounded; length and width equal ; about sixty-six close, round, equal, scaly ridges. 



A handsome shell, with numerous, close, rounded, radiating ribs, each closely set with small, arched, im- 

 bricated scales, not distinctly visible without the aid of a lens, surface evenly convex ; outline nearly circular. 

 I have not seen the ears of this species. Length one inch three lines, breadth one inch four lines. 



Pecten cognatus. M'Coy. (PL XIX. fig. 4). 



Sp. Ch. — Tnmcato-orblcular, depressed ; posterior ear pointed, undefined from the body of the shell; sur- 

 face radiated with about thiity-elght sharp, slender ridges, nearly equal in length and thickness, and separated 

 by flat spaces twice the width of the ribs, crossed by fine, sharp, concentric strlas, about the same distance from 

 each other as the radiating ribs. 



This species resembles the P. megalotis, M'Coy, but is distinguished by the ears being radiated ; the pos- 

 terior ear is also shorter and less acute, and the entire shell wider and more depressed in the present species. 

 Length six lines, width six lines. 



Pecten comptus. M'Coy. (PL XV. fig. 14). 



Sp. Ch. — Longitudinally ovate ; ears equal, anterior rounded, with a deep sinus, posterior pointed, 

 marked with three radiating ridges, crossed by very fine, sharp stri^ ; body of the shell radiated with about 

 forty-six distinct, rounded irregular ridges, intervening spaces flat, smooth. 



This pretty Httle shell occurs in great abundance, in company with the P. irregularis, M'Coy, which it re- 

 sembles in general size and shape, and in the irregular thickness of the radiating ribs, but has nearly twice the 

 number of radiating ridges, making it, of course, appear much more finely striated, even to the naked eye. 

 Length three lines and a half, width tliree lines and a half 



Pecten concavus. M'Coy. (PL XV. fig. 10). 



Sp. Ch. — Orbicular, wider than long; ears nearly equal; left valve concave outwardly; covered by about 

 one hundred and fifty rough, radiating ridges, alternately larger and smaller. 



