TO GEOLOGY. 155 
P. elegantissima. Plate 5. Fig. 161. 
Description. Shell subpyriform, alternate, beautifully 
cancellate over the whole exterior ; substance of the shell 
rather thin ; spire rather elevated, pointed ; suture small ; 
whorls five, convex ; canal rather long ; mouth subovate, 
contracted ; outer lip 
Length .6, Breadth .2, of an inch. 
Observations. One nearly perfect, and several fractured 
specimens of this very beautiful species only have come 
under my notice. Its delicate and graceful form and 
highly adorned exterior render it very remarkable. It is 
closely allied to the preceding species, but differs in having 
a longer canal, in the absence of the angle on the su- 
perior part of the whorl, and in being a much smaller and 
thinner shell. In some of these characters it has a stronger 
resemblance to the Pyrulanezilis (Lamarck). Like it, it is 
without the angle. Its being more attenuate and having 
a higher spire makes it specifically different. The reticu- 
lation is, if possible, more perfect and beautiful than on the 
cancellata. 
P. Smithii.* Plate 5. Fig. 162. 
Description. Shell pyriform, smooth, ventricose, canali- 
culate on the widest part; substance of the shell very 
* T have placed to this species a name which will not soon be forgot- 
ten to British geologists. The veteran geologist William Smith, was 
almost a solitary labourer for mariy years in the field, and to him very 
much is due for the present advanced state of the science of geology in 
