LITHOPOMA. 401 



Ex. P. cffilatum, Chemnitz, pi. 44, fig. 7. Opercu- 

 lum, P. cselatum, fig. 7, a, 7, b. 



In Pachyponia the last whorl is not acutely angulated, 

 and the aperture is somewhat circular; the prominent 

 callus of the inner lip is peculiar, and the operculum is 

 \exj thick and shelly. 



Species of Pachyponia. 



Americanum, Gmel. plicato-nodosutn, Cheyn. 



Cfelatum, Chem. purpuratum, Gmel. 



imbricatum, Gmel. rhodostoma, Phil. 



inaequale, Martyn. sculptum, Phil. 



inerme, Gmel. Sirius, Gould. 



Genus LITHOPOMA, Grav. 



Operculum ovate, thick, thicker at the end, with a 

 broad, thin margin at the outer edge. 



Shell turbinate ; spire elevated, whorls nodulous, axis 

 imperforate ; aperture sub-circular ; inner lip incurved, 

 longitudinally grooved, anteriorly sub-truncate. 



Ex. L. tuber, Linnceus^ pi. 45, fig. 1. Operculum, 

 L. tuber, fig. 1, a, 1, J. 



The absence of umbilicus and the nodulous nature of 

 the whorls, which are not acutely edged around the peri- 

 phery, will serve to distinguish this genus ; the shells 

 have more colour on the outer surface than in the other 

 members of this sub-family. 



Species of Lithopoma. 



Olfersii, Trosch. tuber, Linn. 



saxosum, Phil. tuberosum, Phil. 



VOL. I. -^ F 



