26-4 PROCEEDINGS OF THE ACADEMY OF [1898. 



MATERIALS TOWARD A NATURAL CLASSIFICATION OF THE CYLIN- 



DRELLOID SNAILS. 



BY HENRY A. PILSBRY AND E. G. VANATTA. 



While recording some recent additions to the North American 

 landsnail fauna with the intention of revising the " Check List " of 

 United States land mollusks published in these Proceedings for 

 1889, the attention of the senior author was recalled to the rejection 

 of the generic name Cylindrella by Messrs. Harris and Burrows in 

 1891, and their substitution of a new name for the group. Upon 

 compiling a list of the generic and subgeneric names which have 

 been applied to species of " Cylindrella," it became obvious that a 

 thorough taxonomic revision was urgently needed. In order to as- 

 certain which of the numerous names should be retained as valid, 

 to place these upon a solid basis, and to reduce the remainder to 

 synonyms, it was found necessary to supplement a review of the lit- 

 erature of the group by an examination of the snails themselves, 

 especially with reference to the radula?, and the internal characters 

 of the shells, revealed by a study of sections cut to expose the inter- 

 nal columella or axis. This detailed examination has been made 

 chiefly by the junior author of this paper. 



The characters of the radula have been utilized as a basis for 

 classification by Crosse and Fischer in 1870, their paper marking 

 an epoch in the taxonomic history of this family. W. G. Binney 

 has added to our knowledge of this subject upon the lines laid down 

 by the French writers ; and later, Strebel and Pfeffer, in their sug- 

 gestive and original series of papers upon the Mexican fauna, have 

 made important contributions toward a rational classification of the 

 group. There are many other writings bearing upon the nomen- 

 clature of the Cylindrellas, but no others of importance for original 

 facts or views concerning their phylogeny or structure, aside from 

 mere species work. 



The external conchologic characters of the Cylindrellas are well 

 known by the writings of Pfeiffer, Poey and others, but the modifi- 

 cations of the internal armature have been far less fully elucidated. 

 A portion of PfeifFer's descriptions mention briefly the internal 

 structure, and some of the plates of the Novitates Conchologiece 



