158 Cincinnati Society of Natural Ristoi'u. 



Among the first, the common habitat of the S. spinosum and S. edgar- 

 ianum is between flat rocks, where I have often seen the former con- 

 gregated by hundreds, the dead and living being found together in a 

 common mass. Of similar habit, and associated with them, was the 

 rare P. cumherlandiana, the rocks being apparent!}^ without any mois- 

 ture, and the living snails having an epiphragm over the mouth of the 

 shell, as dui'ing Ij^e winter period of hibernation. The least sliding of 

 the rocks must damage numbers of specimens. 



There is another evidence in favor of the inference which ma}- be 

 drawn from the facts given in this article. The species of Stenotrema 

 not inhabiting such situations, exhibit none of these peculiarities. 

 They vary in size, but there is no abnormal development or depression 

 of the spire, nor any approach to the carinate types. 



The Patula group presents the same fact, as the common P. alter- 

 nata exhibits no wider variations in the mountain regions than char- 

 acterize it elsewhere (the variety mordax not being included). Among 

 the species of Mesodon, Zonites, Triodojjsis^ etc., the cases of abnormal 

 variation are confined to coloration and size, and not to form, except in 

 the case of the T. ohstricta above noted. 



Moreover, in regions remote from these influences, we do not find 

 the number of varieties which here exist, and the species under Siuy 

 type, which are furthest removed from it, will be found in those locali- 

 ties where the liability to some accidental interruption of the ordinary 

 process of growth becomes more frequent. While such circumstances 

 of environment as may arise from sudden changes of climate, abund- 

 ance or scarcity of food, the prevalence or absence of foes, and the 

 multitude of other causes which are usually cited may have assisted 

 in this work, I feel confident that we can trace to the more direct one 

 of habitat the reason for many of the varieties in our Mollusca; 

 nor would I confine these statements to the terrestrial tribes alone, but 

 extend them to the numerous denizens of the mountain streams flow- 

 ing through the same region, that have offered to the ambitious makers 

 of species such an exhaustless fountain from which to multiply syn- 

 onymy and confuse the true seeker after truth. 



The wide range of varieties among the shells collected by Mr. Hemp- 

 hill in the canons of Utah and Idaho, is very suggestive in this con- 

 nection. There are, also, several species from mountain lands in 

 Europe, of whose habits I know nothing, save that they are inhabitants 

 of the Alps, Pyrenees and Carpathians, that differ so far from the type 

 with which they are classed as to point in the same direction. Wheth- 

 er these cases are parallel or not, there is here abundant room for a 

 speculation if for nothing more; and it seems that the weight of evidence 

 is in favor of the suggestions which T have thus hastily indicated. 



