Bmii shells as have a horny with such as have a shelly 

 operculum, we think also a question of some importance; 

 nor can we ascertain whether all those Naticse, which 

 have a callosity in the umbilicus have also a shelly oper- 

 culum or not, nor whether all those which have an horny 

 operculum are also destitute of the callosity in the um- 

 bilicus. The difficulty of ascertaining this point is the 

 consequence of the general carelessness of those who 

 have opportunities, and have not preserved these shells 

 with their opercula. 



Of the numerous recent species which we now admit 

 into Natica, a very few inhabit our coasts, and these all 

 have horny opercula: we certainly have not the N. Can- 

 rena, nor the N. Glaucina of Lam., although both thos(i 

 names are frequently admitted into English catalogues, and 

 Lamarck does no^t appear to have been acquainted with 

 our more common species. The fossil species are also 

 numerous^ and they are remarkable for their near resem- 

 hlance in form to the recent ; some of them even retain 

 their colours : they abound in some of the newer forma- 

 tions above the chalk, especially in the London Clay, 

 Calcaire grossiere, and Craig. We should not hesitate to 

 admit to this Genus as it now stands several shells which 

 Lamarck places among his AmpuUaria, such as the 

 following species; A. acuta, spirata, canalifera, patula,. 

 sigaretina, and probably A. crassatina> hybrida, acumi- 

 nata and depressa. His fossil Natica labellata, and our 

 I'ecent N. glaucinoides resemble each other extremely. 



Fig, I . Nerita Canrena, with its gemicircularly grooved shelly operculum. 



2. Mammilla. 



3. cepacea. Lam., a fossil species iFrom near Paiis^ 



4. Caarena of Brocchi, a fosiii from Piace]iz& 



