500 KEV. G. E. WHIDBORNE ON SOME FOSSILS 



There is a specimen of this shell in the British Museum from the 

 Green bed of the Northampton Sand of Casterton, and it is quoted 

 by Sharp from the Lincolnshire Limestone. 



It is distinguished from P. demissus by its greater width, more 

 symmetrical and equilateral contour, and the shape of the wings. 



Pecten fenestrates, n. sp. Plate XY. figs. 12, 12a. 



Eight valve flatly convex, slightly oblique. "Wings defective, but 

 apparently rather large, and the front one very lobate. Umbo flat, 

 small, acute, and narrow, bounded on each side by long concave 

 edges, over which the surface turns through a right angle and 

 reaches the plane of the wings at about the depth of half a line 

 below them ; these edges reach the circumference of the shell 

 at less than half its diameter from the umbo, the margins then form- 

 ing a regular semicircular curve, a little produced, however, in 

 the infero-anterior direction. The whole surface ornamented by 

 about twenty-five prominent, distant, subacute, straight rays, which 

 have a tendency to alternate, and are crossed by rather more nume- 

 rous and smaller, sharp, fringe-like ridges, forming with the rays 

 small hollows, which are either square or have their shorter and not 

 their longer diameter (as in P. retiferus, M. & L.) in the direction 

 of the rays. The central region somewhat convex, becoming 

 slightly concave near the sides. The inside with ten or twelve 

 smooth rays (as in P. jpersonatus). 



Dimensions of Miglit Valve. Length 11 lines, width 10 lines, 

 depth 1 line. 



There is a specimen of the right valve in the Lycett Collection at 

 Jermyn Street, from Kodborough, and T have obtained similar shells 

 at Dundry, Leckhampton ?, and Bradford Abbas. 



In P. clathratus, where a similar but much finer network occurs 

 on the right valve, the number of rays is more than sixty, and they 

 are all of the same size, slightly but distinctly undulating. The con- 

 centric ridges also are of the same size as the rays, the shell is much 

 longer and less oblique, the marginal curve is greater than a semi- 

 circle, and the side edges by the ears are straight and not so pro- 

 minent. The shell is much flatter, the umbo small and less elevated, 

 and the ears probably larger. 



In the left valve of P. retiferus the rays are rounded on the top 

 and much more numerous, and are cut and broken by the irregular 

 turned-up and lamellar edges of the very distant growth-lines. It 

 is a much more convex and equilateral shell, and the side ridges are 

 indistinct. 



In the present species the difference in the size of the alternate 

 rays is sometimes very marked, and the transverse fringes, being very 

 fine, are often rubbed or broken off. 



Pecten intermittens, n. sp. Plate XY. figs. 13, 13a. 



Right valve somewhat convex, longer than wide. Umbo direct, 

 central, bounded by two low, oblique, straight ridges, which meet 

 the border one half way down the diameter of the shell. Anterior 



