282 Remarks on Certain Specie* of . 



The fact of wide distribution of identical or closely allied 

 forms is admitted, but how far attributable to the physical out- 

 lines of the Continent, or to circumstances connected with their 

 original creation, are subjects of deep interest* 



Very many of the species present great variations, — so much 

 so as to induce difference of opinion as to whether individuals 

 should be considered simply varieties, or valid species. Our 

 knowledge of the limits of variation is very circumscribed and 

 unsatisfactory, and we know little or nothing of the causes of 

 this variation, — whether due to physical circumstances or to 

 creative power. 



Several species have a tendency to run into, or are repre- 

 sented by acutely carinated forms ; H. alternata Say is thus 

 represented by H. Cumberlandiana Lea, H. palliata Say by 

 M. helicoides Lea, H. stenotrema Fer. by H. spinosa Lea, and I 

 may add H. Troostiana Lea by H. fatigiata Say. The metro- 

 polis of the carinated forms seems to be Tennessee. 



The sculpturing and epidermis also greatly vary ; the fine 

 incremental strise of the Ohio H. alternata, are replaced in the 

 South by strongly developed ribs, and in some individuals of 

 H. palliata, the rough epidermis described by Say is wholly 

 wanting. The situation of the teeth on the peristome is by no 

 means constant, especially in II tridentata Say. 



A careful examination of the animals of the varieties of the 

 species would be a most valuable contribution to science, — it 

 would show to what extent variation in the shell prevails, with- 

 out variation in its living tenant. 



The local distribution of varieties renders it most important, 

 in seeking to identify the species of Authors, to learn from 

 whence their specimens were obtained, and to study examples 

 from the same locality. 



* It is worthy of remark, that in the limited area of the Island of Jamaica, the 

 forms of H. acvta Lam. differ as widely as those of H. altei-nata Say, distri- 

 buted over the North American continent from Canada to Texas. 



