94 Quarterly Journal of Corichology. 



the spL om which it was proposed to separate them, they ap- 



parently torgot that the very difference of locality or habitat, with 

 its accompanying condition, caused the variation in question." — I 

 wish to call particular attention to the extract A, as I shall have oc- 

 casion to use it as a test in several cases. First of all, I take the 

 genus Siucinca. This, according to Reeve and Jeffreys, consist of 

 three species, S. piitris, elegaus, and oblonga (Forbes and Hanley 

 make but two). But besides these species, Jeffrey gives two var- 

 ieties of elegans and three oi pittris. Speaking of elega?is, he says, 

 " It forms a passage through its second variety from the last 

 (putris) to the next species (oblonga). The two varieties of elegans 

 are smaller than the type, but this has not anything to do with it, 

 because, as he saySj when speaking of the genus Pisidiiim (page i8) 

 " Size, substance, sculpture, and lustre, are not of much account, 

 as they mainly depend on the chemical ingredients of the water 

 inhabited by the molluscs, as well as their supply of food." His 

 reasoning, of course, is not hmited to any particular genus, but 

 applies alike to all. Now, remembering what was stated above by 

 him, that elegans forms a passage from the first to the third species 

 by its second variety (ochracca). After applying his own test, it 

 certainly appears (A) that these three forms are so " intimately 

 blended together by intermediate links," that they cannot be fairly 

 considered a distinct species. 



Every conchologist is aware of the difficulty of distinguishing 

 some of the species of Zonites. The distinctions between some of 

 them are so very trifling, that it requires much more faith than I 

 am possessed of, to believe that they are really distinct. Z. purus 

 resembles Z. radiatuliis so closely, that Reeve obsei-ves that " A 

 careful application of the lens is necessary to bring out its specific 

 characters in obvious relief" Jeffreys (p. ii6) says, ^'■Z radiatulus 

 resembles Z. purus ' in the size and form of the shell ; but the 

 peculiar sculpture more glossy appearance, and narrower umbilicus 

 of the present species will easily distinguish it from Z. purus. " 

 But he has already stated (p. i8) that "size, substance, sculpture, 

 and lustre, are not of much account." And we shall see as we 

 proceed to another genus, that these very distinctions are not 

 even allowed to constitute a variety. Few shells have been 

 the cause of greater controversy than Helix nemoralis, and 

 hortensis : are they distinct species or not ? Gray, Norman, and 

 others, unite them. Jeffreys (p. i88) says he never found 

 H. nemoralls and hortensis living together, and in speaking of a 

 variety of Limncea palustris (p 114), he says, as a reason for not 

 considering it a species, " that it is not found in company with 

 any other form." I do not clearly understand this reasoning. Then 

 supposing H. nemoralls and hortensis to be found together (as they 

 certainly may be), it would appear to prove that they were speci- 

 fically distinct, even taking Jeffrey's own definition of a species, 

 which is a group of individuals which resemble each other as well 



