TO GEOLOGY. 161 



England. Eleven have been described by Sowerby, Phil- 

 lips and Mantell, one as low as the Inferior Oolite. The 

 highest are in the London Clay, where five species have 

 been observed by Mr Sowerby. M. Deshayes gives eight 

 for the Tertiary. No species has heretofore been observed 

 in this country to my knowledge. 



FAMILY PURPURIFERA. 



GENUS MONOCEROS. Lamarck. 



M. pyruloides. Plate 5. Fig. 166. 



Description. Shell turbinate, inflated, transversely and 

 indistinctly striate above and below ; substance of the 

 shell thick ; transverse furrow linear, with indistinct 

 angular points ; spire short ; suture small ; whorls five, 

 convex ; umbilicus rather large ; mouth ovate, narrow ; 

 columella thickened ; outer lip sharp. 



Length .7, Breadth .5, of an inch,-- 



Observalions. This species is remarkable for its turbi- 

 nate form. The superior part of the mouth is much 

 thickened. It may be objected to, that this and the two 

 following species should be placed in the genus Monoceros, 

 as none of the specimens observed have the seat of the 

 horn perfect. This part is therefore not described. I 

 am satisfied nevertheless as to the genus; for the groove 



