221 
I have very lately been so fortunate as to obtain another fossil of this 
species : it very nearly resembles, in its form, the fossil which is here 
figured ; but is rather larger, and is invested with its shell. 
Mr. H. H. Goodhall, of the East-India House, whose kind assistance 
I have had repeated occasion to acknowledge, favoured me with the 
valve of a small shell, which he picked up in a marle-pit near Shefford, 
in Bedfordshire. The upper and under side of this valve is represented 
Plate XV. Fig. 6 and 7- It is undoubtedly of this genus, and apparently 
a different species from the fossil, or from either of the recent shells. 
CXLIII. Placuna. An irregular, free, flat bivalve : the internal 
hinge formed by two diverging ridges, in the form of a V, and serving 
for the attachment of the ligament. 
The shells of this genus were placed by Linnaeus in the genus 
Anomia, from the shells of which they differ in almost every respect. 
They are generally flat and rounded, or nearly quadrangular, thin, 
fragile, demi-transparent, and shining. The superior valve is larger 
and more tumid than the inferior. The shells described by Linnaeus, 
which may be placed under this genus, are Anomia 'placenta and A. 
sella ; but Bruguiere has figured six species. I am not acquainted 
with any British fossil of this genus. 
CXLIV. Harpax. An adherent, oblong, and somewhat triangular, 
inequivalved shell; the hinge formed by two long, diverging, crenulated 
teeth in one valve, and four in the opposite, disposed in the form of a V: 
the upper valve, armed with pointed hooks : one mark of attachment. 
The only shells of this genus that I have seen, I found about three 
feet below the surface at Leonard Stanley, in Gloucestershire. These 
shells are of an oblong, and somewhat of a triangular form. The one 
valve, which is convex, is rugously plicated, anddivided by slight, trans- 
verse, curved ridges ; and the other, which is flat and thicker, is beset 
with long pointed and hooked processes, lying longitudinally in trans-i 
verse rows. The hinge is formed by two long projecting teeth, trans- 
versely crenulated on both sides, and diverging in the form of a V. on 
