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A very beautiful Pecten is found in the green sand of Wiltshire, of 

 which a very correct representation is given by Lister, Conch. Tab. 470, 

 Fig. 28. 



It is an equivalved, slightly orbicular shell, both valves being rounded: 

 it is ornamented with about seventy-two roundish radii, which are muri- 

 cated with tubular squamae : twenty-four larger radii, having two or 

 more smaller radii disposed on each side. In some specimens, and par- 

 ticularly in the superior part of the shell, the intervening smaller radii 

 are more numerous. The ears are marked with oblique, curved rugse. 

 The beauty of this fossil, derived from the richness of its ornamented 

 surface, is not all that renders it interesting : the substance of which it is 

 formed cannot fail to excite a considerable degree of admiration. It is 

 completely silicious, and even in some parts transparent; and yet the 

 minutest parts of its markings do not appear to have suffered any altera- 

 tion in their, form from this change. 



One of the most interesting fossils of this genus, which I possess, is the 

 greater part of a fragment of an upper valve, with angulated ribs, im- 

 bedded on chert ; and which, although so changed as to be now highly 

 silicious, still retains a considerable portion of its original colour. 



A singular Pecten is found near to Thame, in Oxfordshire, imbedded, 

 as I have been kindly informed by Mr. Lupton, of Thame, in a green 

 silicious sand, resting on an indurated clay, at nearly sixteen feet from 

 the surface. This is an auriculated shell, about three inches in diameter, 

 and nearly circular : both valves are marked with regular, transverse, 

 concentric, imbricating ridges, and both convex; but the upper one less 

 so than the lower. A Pecten, of half the size of the preceding, with 

 much stronger concentric ridges, is found in the valley of Ronca. 



In Gloucestershire is frequently found a Pecten, which, in many spe- 

 cimens, has attained a considerable size, six or seven inches in diameter. 

 These shells, at least the specimens which I possess, have twenty-four 

 nearly smooth roundish radii, with very faint transverse lines of growth 

 running over them and the intervening sulci. The ears appear to be 



