02 SYNOPSIS OF THE CHARACTERS OF THE 



The difference between this species and the P.fallax, M'Coy, is very obvious, both valves being radiat- 

 ingly striated in the latter, while only one is in the present species. The space intervening between the ribs is 

 smooth ; the ears small. 



Pecten duplicicosta. M'Coy. (PL XV. fig. 9). 



Sp, Ch. — Longitudinally ovate, depressed ; ears nearly equal, pointed, marked with numerous, close, rough, 

 radiating ridges ; surface radiated with very numerous, close, fine ridges, disposed in pairs. 



This species is unlike any other Pecten with which I am acquainted, in the disposition of its striae : when 

 shghtly worn or rubbed, each of the fine, flat, radiating ridges seems doubled, or divided by a fine mesial line. 

 Length seven and a half lines, width seven Unes. 



Pecten ellipticus. Phil. 



Pecten elHpticus. Pkil. Geol. York. 



Sp.Ch. — Elongate, ovate, convex, smooth; ears small, equal, square. 



This species is distinguished from the P. Sowerbii, M'Coy, by its smooth surface, and having ears of the 

 usual form, not raised above the beak of the shell ; traces of the colouring frequently remain in tliis shell ; 

 it seems to have been dark zigzag markings, on a light ground. Length one inch two lines, width eleven hnes. 



Pecten elongatus. M'Coy. (PI. XVI. fig. 9)- 



Sp. Ch. — Longitudinally oval, length one-sixth greater than the width, convex; surface minutely striated 

 concentrically ; ears nearly equal, [one square, sUghtly defined, the other rounded, deeply separated from the 

 body of the shell. 



This fine species appears smooth to the naked eye, but in finely preserved specimens, or with the aid of a 

 lens, very minute, regular, concentric striie are visible ; from the P. Sowerbii, M'Coy, which has somewhat si- 

 milar striae, it is distinguished by its greater size, and the form of its ears, while from the P. filatus, M'Coy, 

 which to the eye appears nearly as smooth, and has the same general form, it is distinguished by having the 

 minute striation concentric, instead of longitudinal, as in that species. Length one inch seven lines, width one 

 inch six lines. 



Pecten exiguus. M' Coy. ( PI. XV. fig. 1 1 ). 



Sp. Ch. — Longitudinally ovate, slightly convex ; ears large, distinctly marked, nearly equal in length, pos- 

 terior one pointed, anterior one narrow, rounded at the end, deeply divided from the body of the shell ; both ears 

 marked with radiating ridges, crossed by sharp, concentric strias ; body of the shell marked with exceedingly 

 fine, close, radiating strias. 



Tliis is the smallest species of Pecten with which I am acquainted ; the stria on the body of the shell are so 

 fine that most specimens appear smooth to the naked eye. It is very common in some locaUties. Length one 

 and a half Hnes, width slightly less. 



Pecten fallax. M'Coy. (PI. XIV. fig. .2). 



Sp. Ch. — Nearly orbicular, convex; hinge-line exceeding the width of the shell; ears unequal; surface of 

 one valve with numerous rounded, nodulous ribs, alternating irregularly with very thin, smooth ones ; interve- 

 ning spaces striated transversely; the other valve with numerous, radiating, smooth, equal ribs, the spaces 

 between which are also smooth. 



This species is remarkable for the difference it exhibits between the right and left valves, the one 

 being covered with thick, nodulous, radiating ridges, which even cover the ears ; between each pair of those 

 there is usually a very fine, smooth rib, the intervening spaces being sharply striated across ; the opposite valve, 

 on the contrary, has much more numerous equal ribs, which, with the intervening spaces, are quite smooth. It 



