TO GEOLOGY. 103 



Observations. This species differs from those which pre 

 cede it, in having transverse stria}. The whorls are inflated, 

 while the others are flat. 



P. sulcata. Plate 4. Fig&quot;. 84. 



Description. Shell conical, largely and transversely sul- 

 cate above ; substance of the shell thin ; apex obtuse ; suture 

 furrowed ; whorls five, flattened ; mouth subelliptical, one 

 third the length of the shell ; columella flattened at the 

 base ; margin thickened above. 



Length .1 , Breadth l-20th, of an inch. 



The smaller figure is of the size of nature. 



Observations. A very minute species, remarkable for its 

 large furrows, which become obsolete on the lower part of 

 the whorls. It differs from striata in being less elevated, 

 as well as in having furrows. 



P. umbilicata. Plate 4. Fig. 85. 



Description. Shell elevated above, rounded below, sub- 

 carinate, polished; substance of the shell thin; apex acute ; 

 suture linear; umbilicus large; whorls nine, flattened; 

 mouth subovate, acutely angular above, one fifth the length 

 of the shell ; columella incurved at base ; margin entire. 

 Length .2, Breadth .1, of an inch. 



The smaller figure is of the size of nature. 

 Observations. This smooth arid polished species differs 

 from the above in being umbilicate. Its umbilicus is wide, 



