NERITA^ 



having a thin epidermis; mostly flattish beneath, without 

 any umbilicus; spire; very short. Aperture semicircular; 

 inner lip mostly flattened, rather sharp edged, most 

 commonly toothed, its edge oblique to the axis of the 

 shell; outer lip sharp edged, crenulated or toothed on 

 the inner side. A little prominence is observable just 

 within the shell at the lower end of the inner lip, between 

 which and the inner lip the little appendage to the oper- 

 culum slides as it opens, or closes the aperture for the 

 ingress or egress of the animal; and it is remarkable 

 that this operculum opens as a door upon its hinges for 

 the animal to pass out : Lamarck says it is sometimes 

 shelly, sometimes only horny; all that we haye seen are 

 shelly. 



The shells here included under Nerita form only a 

 part of that Genus according to Linneans; there are 

 many recent species which are marine, but as we cannot 

 include the one commonly called N. littoralis, we do not 

 know of any British ones, and though we are acquainted 

 with several fossil species, they are rare, and as we believe 

 only occur in the London Clay and corresponding fprma-^ 

 . tions. 



The little shell commonly found in the StonesHeld 

 slate, and referred to this Genus, should, as we think, 

 go with N. littoralis ; and probably our present fig. 5, with 

 Turbo littoreus, from which they only differ specifically. 



Jig. 1. Nerita Peloronta with its operculum. 

 3. The inside of the operculum. 



3. Nerita chlorostoma ? Lam. 



4. We believe to be undescribed and have therefore called it N. ornata, 

 testa subglobosa, transversim sulcata, albo vel luteo-nigroque variegate, spir4 

 promiaula; labio interno quadridentato, superne rugoso.* 



5. Nerita gpanulata, Z)efr. 



6. tricarinata, , a fossil species from Hauteville in Normandy,. 



* We once thought this was the N. Histrio of Linn., but the descriptions of 

 that species are so variable, and the figures cited so bad, that it is impossible to 

 ascertain it with certainty. 



