98 SYNOPSIS OF THE CHARACTERS OF THE 



Pecten planicostatus. M'Coy. (PL XIV. fig. 6). 



Sp. Ch. — Obliquely obovate, slightly convex; ears short, square, unequal, smooth; surface wth very 

 broad, iiTegular, smooth, flattened, radiating ribs, from the beak. 



I have much doubt whether this shell really belongs to the genus Pecten — it is at least an aberrant type, 

 and if placed in this genus it leads to Lima, and if placed in Lima, it leads back to the present genus. The 

 hinge-line is oblique, the ears short, smooth, and slightly unequal ; the surface of the shell is marked with 

 very broad, smooth ribs, much flattened, and dividing irregularly as they approach the margin, where they are 

 about twenty in number. Length one inch three lines, width one inch four lines. 



Pecten PLANOCLATHEATUS. MCoy. (PI. XVI. fig. 2). 



Sp. Ch. — Longitudinally ovate, convex, reticulated with numerous, equal, longitudinal, and concentric, 

 broad, flattened ridges. 



This species appears to be exceedingly rare, only one specimen being as yet known, and even that one is 

 imperfect as to the ears ; the species is, however, easily known from any other by the flatness of the ridges. 

 Length ten lines, width nine lines. 



Pecten plicatus. Sow. 



Pecten plicatus. Sow. Min. Con. 



Sp. Ch. — Nearly orbicular, oblique, depressed ; ears large, unequal, surface covered with fine, smooth, 

 flattened, irregular, radiating strise. 



This species is closely allied to the P. papyraceus, but has much smaller ears, and coarser striae. 



Pecten polttrichus. Phil. 



Pecten polytrichus. Phil. Pal. Foss. 



Sp. Ch. — Transversely elliptical, twice as wide as long; surface radiated with deep, sharp sulci, between 

 which are from six to nine finer radiating strife. 



The character of the striatiou of this species resembles that of the Orthis interstrialis. I have never seen 

 specimens shewing the ears. 



Pecten quinquelineatus. M'Coy. (PI. XVII. fig. 6). 



Sp. Ch. — Longitudinally oval, nearly flat ; surface slightly irregular, marked with about thirty-five narrow, 

 uneven, radiating ridges, each pair having usually between them five smaller, radiating strise, the middle one 

 of which is largest, interstitial spaces flat; (ears unknown). 



This fine shell at once strikes the eye, from its great size and regularly oval contour ; the principal radiat- 

 ing ridges are strong and direct, but narrow ; the intervening striae are almost invariably five, but in one or two 

 instances near the sides there are only three ; of these the middle or odd one is always larger than the others. 

 I have not seen the ears of this species. Length four inches two lines, width four inches. 



Pecten rugulosus. M'Coy. (PL XVII. fig. 7). 



Sp. Ch. — Orbicular, slightly convex ; ears distinct, nearly equal, anterior rounded, deeply divided from 

 the body of the shell, marked with four distant, radiating ridges ; posterior slightly pointed, marked with three 

 or four rounded, radiating ribs ; body of the shell with numerous close-set, radiating strise, alternately larger 

 and smaller, slightly nodular or roughened. , 



This species, has little to attract attention, either in its fonn or markings, the distinct, radiating ridges on 



