OF CONCHOLOQY. 83 



ON THE MODERN CLASSIFICATION OE MOLLUSKS. 



BY O. A. L. MdRCH. 



[From "Journal de Conchyliologie, October, 1865.] 



TRANSLATED BY GEORGE W. TRYON, JR. 



In a Review of my Catalogue of the Lassen Collection, M. 

 Crosse has cited, as an example of the inferior value of the 

 lingual dentition, as a systematic character, the fact, that the 

 Helicinse, according to this classificatioD, are placed with a 

 much elongated group — the Cyclostomse. These two families 

 have not, really, another character in common, than the posi- 

 tion of the eyes at the exterior base of the tentacles, a char- 

 acter partaken of by nearly all the tentaculated Gasteropods. 



The Helicinse are distinguished by the want of the profound 

 groove in the middle of the foot, and especially by the form 

 of the operculum, which, on the contrary, accords perfectly 

 with that of the Neritinse; nevertheless, they have not the 

 resemblance of the lateral processes. The callosity of the 

 columella, as also the faculty of dissolving the internal walls 

 of the shell, are also characters which indicate resemblances 

 with the Neritinse. As well as ail fiuvatile, univalve or bi- 

 valve shells have certain common affinities, for example, a 

 thick and coriaceous epidermis, so have the Helicinse charac- 

 ters in common with other terrestrial Mollusks, such as the Cy- 

 clostomse, and especially the Helices. 



It is M. Loven who first founded the modern classification 

 of Gasteropods, based on the lingual dentition. M. Troschel 

 has given names to several groups established on this charac- 

 ter {Tsenioglossata, Rhipidoglossata, Toxoglossata, etc.); but he 

 has, at the same time, admitted others, based on the organs of 

 respiration (Pneumonopoma, Cyclobranchia, etc.) My studies 

 of Mollusks during twenty years, have induced me to accord 

 a more elevated systematic value to the lingual dentition. 

 Certain exceptions can, of course, be cited, as well as the 



