NERITOPSIS. 



TESTA obovata, spira brevi, anfractibus paucis, 

 rapide majoribiis, superficie plerumque gra- 

 nosa ; apertura transversa, suborbiculari, peri- 

 tremate intus incrassato, margine acutiusciila ; 

 columella prope inedium late emarginata. 



A Genus of marine shells of which several species are 

 known, both recent and among the tertiary fossils. The ' 

 principal species has been long known and described 

 under the name of Nerita cancellata in Chemnitz, but 

 Lamarck has placed it with Sigaretus. We have also 

 given one of the fossil species among our Neritae. It 

 appears to belong to the same family as the Naticae and 

 Neritae, but we are not aware of its having any operculum, 

 although we are much disposed, judging from the pecu- 

 liarities of the inner edges of the aperture, to believe that 

 it has. 



The species of this Genus are of an obovate form, with 

 a very short spire consisting of not more than three or four 

 volutions appearing to increase very rapidly in size, and 

 approach in shape very nearly to that of many Naticae, 

 their external surface is however for the most part rough 

 with transverse rows of grains. The aperture is entire, 

 transverse, somewhat orbicular, its peritreme being 

 thickened within and generally somewhat grooved and 

 its outer edge rather sharp; on the columellar side 

 however there is a broad, and as it were double, rounded 

 edged notch rather before the middle, and it is in this 

 peculiarity that it differs most materially from Natica, and 



