[iv.] 



separatiag, according to supposed important characters of the 

 soft parts, species which, conchologically, greatly resemble one 

 another, and again, on the same grounds, uniting incongruous 

 forms* 



As nearly all the proposed genera of the An ericau Helices 

 appear to be well founded upon differences oi animal ana 

 shell, I have adopted theni, 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 whj desire to become, Cunchologists, 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 

 characters of minor importance, and those, especially, which 

 require microscopic observation, should be generally omitted, 

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



* Several recent writers have separated from the Helicidm certain species, 

 which otherwise are entirely unclistinguishable from that family, on account 

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

 genera Ariun and ParmaceUa. They have accordingly united them either 

 to Arioniam or ParmacelUdm 



The late M. JIoquin-Tafidon, a most excellent French malacologist, 

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

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

 cies within the family Helicidm. 



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

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

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

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

 t-iese animals have not yet been examined; so that, at present, it would 

 servo no useful purpose to use this distinction in classitieation. 



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

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

 tion ot the genera of tlio Hehces into sub-families, several of which appear 

 to form good natural divisions, as llelici-llinoi for tliu thin, glabrous species 

 with unreflected lip. HeUciiia\ on tlie contrary, includes a heterogenous 

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

 should be separated, though I do not think they can p<.s-sibly be correctly 

 associated with Yallonia and PluvriDpifd, :>,trobiln and Helicodiscus. 



A close study of all that has beeu^ accomplished by American malacolo- 

 gists convinces me that — 



1. If the sub-families proposed are properly characterized, i. 6., are natu- 

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

 perly distribute all the species among them, and — 



2. For this reason, other sub-families must remain to bo characterized ; 

 but— 



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

 the at present uimrrarigeable groups of species, it d'.es not sliow the exist- 

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

 defined, exist. 



I'he able investigators, Messrs. Binney, Bland and Morse, wuo are now 

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

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

 choiogical students. Meanwhile, impressed by tlie unsatisfactory nature 

 ot our own edifice feciually with that erected by our predecess .rs), we trust 

 that it will remain unquoted by future systematisls. 



