132 CONTRIBUTIONS 



which will designate with certainty the genus. I would 

 further remark, that there have been no Cerithia yet found 

 in the beds of this locality, although they abound in Eng- 

 land, and on the continent, in the Tertiary, from which for- 

 mation M. Deshayes gives two hundred and twenty species. 

 In the Paris basin alone there are one hundred and thirty- 

 seven species. That there should not yet have been a 

 single true Cerithium observed in the bed at Claiborne is 

 certainly a curious and interesting fact. 



GENUS PLEUROTOMA. Lamarck. 



P. calata. Plate 4. Fig. 123. 



Description. Shell fusiform, turrited, carinate, longitu- 

 dinally folded, covered transversely with minute striae; 

 substance of the shell thick ; apex acute ; whorls eight, 

 subcanaliculate above; mouth narrow, nearly half the 

 length of the shell. 



Length .8, Breadth .3, of an inch. 



Observations. This species is remarkable for its fine 

 transverse striae, which resemble the finest engraving. 



P. Lonsdalii* Plate 4. Fig. 124. 



Description. Shell fusiform, turrited, longitudinally 

 folded, transversely and faintly striate, substance of the 



* Named after the intelligent and efficient curator of the Geological 

 Society of London. 



