TO GEOLOGY. 97 



species. It appears, however, to be a thinner shell than 

 either, and to be less tuberculated. These tubercles are 

 disposed to be spinous and open at the top ; and in some 

 specimens are obsolete. 



Of this genus, six species have been observed in the 

 Tertiary strata of England. One in the Plastic Clay, 

 three in the London Clay, and two in the Crag. M. Des- 

 hayes does not recognise the genus. In this country, it 

 has not, I believe, before been observed in a fossil state. 



GENUS CREPIDULA. Lamarck. 



C. cornu-arietes. Plate 3. Fig. 77. 



Description. Shell elliptical, very convex, longitudinally 

 curved ; substance of the shell rather thick ; diaphragm 

 rather large and somewhat thick ; beak elevated, produced, 

 curved outwards and backwards ; margin oblique, the ele- 

 vated side being on that of the beak. 

 Long. diam. 1.5, Transv. diam. .7, Height .6, of an inch. 



C. lirata ? Conrad. 



Observations. This fine species differs much from any 

 recent or fossil one with which I am acquainted. Its ob- 

 lique margin, and its elevated, produced beak resembling 

 the prow of a Roman galley, eminently distinguish it. It 

 differs from C. costata (Morton), in being more elliptical, 

 convex and produced in the beaks. 



N 



