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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, bothvalves being rounded: 
it is ornamented withabout seventy-two roundish radii, which are muri- 
cated with tubular squamee ; 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 rugae. 
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 
alteration 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 aconsiderable 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 
