222 
the flat valve ; and by four diverging raised teeth on the convex valve ; 
the latter being so disposed, and so crenulated on their inner surfaces, 
as exactly to receive, as in the Trigonia, the teeth of the opposite valve. 
Aware of the danger of unnecessarily multiplying genera, I was at 
first disposed to consider this shell as a species of Trigonia : from this, 
however, I was precluded, on discovering that, unlike the shells of 
that genus, these were adherent — a difference, undoubtedly, sufficient 
to prevent their being disposed under the same genus. 
Plate XII. Fig. 14, represents the internal surface of the flat valve ; 
and Fig. 1 6, a magnified view of its hinge-teeth. Fig. 15 is the internal 
surface of the convex valve, and Fig. 1/ a magnified view of its hinge- 
teeth. Fig. 18 is a magnified view of the outside of the flat valve, 
showing those strong hooked instruments, from which it has presumed 
to give a name to the genus. One specimen of the upper valve of this 
shell manifests a very considerable degree of lustre. 
CXLY. Pecten. A regular, eared, inequivalved bivalve, with con- 
tiguous beaks. The hinge toothless, the pit trigonal, receiving the 
internal ligament. One muscular impression. 
Of those which are in my collection, I much regret the being totally 
uninformed of the locality of most of them. This I particularly regret 
being the case with a specimen which has been imbedded in a hard 
whitish lime-stone, and which is in every respect analogous with P. 
jacobeus, List. Conch. 1 65, f. 2, 166,/’. 3, having, on the lower valve, 
fourteen angulated rays, longitudinally striated : the sulci transversely 
striated : the upper valve having the rays rounded and striated trans- 
versely. Thus is it also with a most perfect specimen of P • radula 
and P. varius, differing in no respect from 0. radula and 0. varia, 
Linn, except in each being of a small size. 
Lamarck particularizes three species found in the neighbourhood of 
Paris : P. plebeius, P. infumatus, P. squamula. In the Harwich cliff 
are specimens found, which I think are referable to the two former of 
these species. 
