CHAP. VIII. 



THE NATICID^, OR NERITS. 



239 



incertitude regarding the many earlike shells belonging 

 or related to the genus Sigaretus of authors^, but of whose 

 animals we know little or nothing. The reader wiU, 

 therefore, understand that the only groups we consider 

 to be natural in the following arrangement, are those of 

 the NeritincB and the NaticincE; the three others being 

 merely conjectural. If the animal of Cuvier's Sigaretus 

 is like that of De Blainville's, we should thus refer it to 

 the group which contains Chelinotus ; but we strongly 

 suspect that the shells of the Sigareti figured by Sowerby* 

 all belong to, and form the typical group of, the present 

 family : Lamarck's Natica constitutes the second ; and 

 the Linnaean nerits the third : the other two may pro- 

 bably be represented by the CryptostomcB of Blainville 

 and Quoy ; and the fifth, which forms the passage to the 

 Turbidcp, either by Lacuna, Turton, or more probably 

 by such long-spired types as Truncatella, Lowe. Of all 

 these, as shells, it may be said generally, that they are 

 globose and turbinate ; the spire being always very slightly 

 developed, the aperture large and semilunar, and the 

 operculum, where it exists, either shelly or horny. They 

 are moderate-sized shells, mostly marine, and are never 

 perlaceous. In the Neritincs, which approach nearest 

 to the HaliotidcE, the spire is sometimes nearly or quite 

 obsolete ; but in the Naticince it is more developed and 

 ventricose. The Neritina', by the teeth on their pillar, 

 and excessively short spire, represent the Volutida ; and 

 Cryptostoma, the LimacincB, or terrestrial slugs. What 



Genera of Shells. 



