NERITINA. 



Lam. Hist. Nat. des Anim. sans vert. VI. pt. 2. p. 182. 



TESTA tenuis, semiglobosa vel ovalis, subtus 

 planulata, non umbilicata. ^pertura semiro- 

 tunda; labio columellari planulato, margine 

 aciitiusculo subrecto, plerumque denticulate; 

 labio ejcterno intus nee dentate nee crenulato. 

 Operculum testaceum, semicirculare, interne 

 appendice lateral! instructum. 



We entirely concur with Lamarck in the reasons which 

 induced him to separate this from the Linnean Genus 

 Nerita, although no former writer had thought proper to 

 distinguish them. Difference of habits, according to 

 Lamarck's hypothesis would necessarily produce divei'sity 

 of characters, and the prosecution of the enquiry has 

 proved that there do exist such peculiarities in the Neri- 

 tinae, besides their being inhabitants of fresh water, as 

 are sufficient to distinguish them from the Neritae in any 

 situation, even in a fossil state as inmates of formations 

 of doubtful origin. We shall, however, proceed to detail 

 the peculiar characters of Neritina, and then endeavour 

 to show in what particulars it differs from Nerita. 



The Neritinse are rather thin shells, generally smooth 

 on the outside, frequently covered with a strong horny 

 epidermis of a pale brown to a quite black colour; in 

 general their spire is very short, sometimes it is almost 

 concealed, in a very few instances they can scarcely be 

 said to have any, and it is very seldom that they have a 

 prominent pyramidal spire. The aperture is semicircu- 

 lar, the inner or columellar lip more or less flattened, 

 its edge, which is placed obliquely to the axis of the shell. 



