TO GEOLOGY. 125 



of its aperture. Lamarck's description of Planorbis nitidu- 

 lus gives the characters of this shell with the exception of 

 the reflected margin. If our shell were fresh water there 

 certainly would not be any necessity to remove it from the 

 genus Planorbis, unless the reflected margin should be 

 considered a character sufficiently distinctive. In 4,he 

 description of the Planorbis, Lamarck says " margine nun- 

 quam reflexo." 



GENUS TURBO. Linnaus. 



T.naticoides. Plate 4. Fig. 114. 



Description. Shell rather convex, smooth ; substance 

 of the shell thick ; suture linear ; umbilicus small ; whorls 

 four ; mouth very round ; outer lip edged. 

 Length .2, Breadth 7-20ths, of an inch. 



Observations. This little species has somewhat the as- 

 pect of a Natica. It seems to have no striking character- 

 istic, but I cannot identify it with any described species. 

 One of the specimens is somewhat polished. 



T.nitens. Plate 4. Fig. 115. 



Description. Shell rather depressed above, flattened be- 

 low, polished ; substance of the shell thick ; suture linear ; 

 umbilicus rather large and round ; whorls four ; mouth 

 suborbicular, outer lip edged, thickened at its superior junc- 

 tion with the whorl. 



Length 3-20ths, Breadth 5-20ths, of an inch. 



