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 marie-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. 



CXL1II. 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 morettumid 

 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. 1 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, and divided 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- 

 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 



