82 Mr. Swainson on Achatinella, 



nature, are evanescent and perishable; defying all artificial 

 preservation of their genuine form, and leaving the inquirer 

 no other object to speculate upon, than an empty, inanimate 

 covering. 



It has, nevertheless, been found, in proportion as a more 

 correct knowledge of these beings has been slowly acquired, 

 that a general uniformity of structure in the shells of any par- 

 ticular group, is so frequently accompanied by a corresponding 

 similarity of organization in the animal, that little doubt can 

 remain of this being, with certain limitations, a general rule: 

 and that although we may be totally ignorant of the precise 

 nature of the one, yet that we are perfectly justified, by analo- 

 gical reasoning, to class and arrange its shelly covering in an 

 artificial system ; waiting for that knowledge, which will here- 

 after give us a more accurate insight into its natural affinities. 



The truth of these remarks will appear very obvious, on 

 looking to the genus Helix, as it was left by LinnjBus, and as 

 it was considered only a few years back ; when the French writers 

 (who have been foremost in the necessary task of forming new 

 divisions) still considered it only in the light of a genus, con- 

 taining many hundreds of species. The illustrious Lamarck 

 perceived the utter uselessness of such a classification ; he seized 

 upon the most prominent types of form, and at once gave them 

 a character and a name. The peculiar views of M. Ferussac 

 led him, in the first instance, to return to the old arrangement, 

 so far as to consider these shells merely as a genus, divided into 

 subgenera, sections, &c. This view, however, he seems at length 

 to have gradually abandoned ; and virtually to admit what, in- 

 deed, is quite obvious — ^that they constitute a family, and a very 

 extensive one, comprising numerous minor groups, or genera, 

 many of which rest on striking dissimilarities in their animals, 

 and all on certain and obvious characters in the shell. 



Th^ great error which, until lately, methodists have fallen 

 into, has been that of considering no group in the light of a 

 genus, unless its limits, or separation from that which was sup- 

 posed immediately to follow it, could be clearly defined. This 

 notion, still very prevalent among continental naturalists, has 

 been fast losing ground in this country, since the Avritings of 

 Macleay have thrown a new light upon the economy of nature, 



