[iv.] 



separating, according to supposexl important cLaracters of the 

 soft parts, species which, conchologically, greatly resemble one 

 another, and again, on the same grounds, unitii^g incongruous 

 forms* 



As nearly all the proposed genera of the An erican Helices 

 appear to be well founded upon differences oi animal and 

 shell, I have adopted them, believing that they will facilitate 

 rather than embarrass the investigator. 



Finally, I may be permitted to add, these pages being writ- 

 ten, not so much for the use of those who are, but rather for 

 those wh ) desire to become, Conchologists, it has seemed to me 

 most proper that the descriptions of 'species should be as con- 

 cise and as free from technical words as possible ; that even 

 cliaracters of minor importance, and those, especially, which 

 require microscopic observation, should be generally omitted, 

 or only slightly alluded to; that the would-be naturalist 



* Severalj'ecent writers have separated from the Uelicidce certain species, 

 wliicli otlierwise are entirely undistiuguisliable from that family, on account 

 of the animal possessing a mucous pore near its tail, like the snails of the 

 genera Avion and Parmacella. They have accordingly united them either 

 to Ai'ioniiHV or Parmacellidce. , 



The late M. jMoquin-Tandon, a most excellent French malacologist, 

 appears to us to« have correctly determined the presence of a developed 

 spiral shell as of sufficient importance to justify the retention of these spe- 

 cies within the family llelicidm. 



The possession of this mucous pore does not appear to characterize the 

 animals of anj'' particular groups of our species, for in those most nearly 

 allied it is absent in one and present in another, and of a well characterized 

 group of species, one only has been found to possess it. Very many of 

 tiese animals have not yet been examined; so that, at present, it would 

 serve no- useful purpose to use this distinction in classification. • 



The ditfercnces in the jaw (buccal plate) and the armature of the tongue 

 (lingual dentition) are employed by lecent investigators for the combma- 

 tion or the genera of the Helices into sub-families, several of which appear 

 to foi'm good natural divisions, as Helicfllinu! for the thin, glabrous species 

 with unreflected lip. 'IleliciiM', on the contrary, includes a heterogenous 

 collection of forms, from which I would suggest that the species of Fatula 

 should be separated, though I do not think they can possibly be correctly 

 associated with Yalloidd and Pkinonpirc, Nrohila and Helicodiacus. 



A close study of all that has been accOn)plished by American malacolo- 

 gists convinces me that — 



1. If the sub-families proposed are properly characterized, i. e., are natu- 

 ral groups, it is impossible, with our present limited knowledge, to pro- 

 pei'ly distribute all the species among them, and — 



3. For this reason, other sub-families must remain to be characterized ; 

 but— 



3. If, when we obtain a knowledge of the characters of the soft parts of 

 the at present unarrangeable groups of species, it d'.es not show the exist- 

 ence of other sub-families, then, in all probability, no sub-fainilies, as now 

 defined, exist. 



The able investigators, Messrs. Binney, Bland and Morse, wno ai'e now 

 carefully and thoroughly studying the dentition of our species, will doubt- 

 less, in due time, arrive at results in the highest degree satisfactory to cnn- 

 chological students. Meanwhile, im])ressed by the unsatisfactory nature 

 of our own edifice Cequally with that erected by our predecess.jrs), we trust 

 that it will remain unquoted by future systematists. 



