214 

 SOLARIUM. 



TROCHUS PERSPECTIVUS. LilinCBUS. 



Chem. 5, t. 196, /. 1691, 1696. 



Linnjeus and other writers considered this genus to be 

 a species of Trochus, with which it certainly appears 

 closely allied, particularly when compared with such of 

 them as have the base terminating in a sharp edge at 

 the outer circumference. In form this genus also some- 

 what resembles the Planorbis, and from the examina- 

 tion of some fossil species it is very difficult to draw a 

 distinct line between them. The division however 

 now made by Lamarck, cannot be mistaken for either 

 of the above mentioned genera, the umbilicus of the 

 shell being always dentated or crenulated at the edge 

 of the internal whorls. These shells arc of an orbicular, 

 depressed conical form, umbilicus very wide, with den- 

 tated spiral whorls running interiorly from the Summit 

 to the margin, the opening of the mouth nearly quad- 

 rangular: no columella. The writer has seen a calca- 

 reous operculum, said to belong to a shell of this ge- 

 nus, but cannot vouch for its having been found with 

 it. In appearance it nearly resembled the thick stony 

 operculum of many of the Turbines, but was of a more 



