124 Remarks oti Certain /Species 



The tendency of species, in different groups of the same 

 genus, to vary as regards form in a similar direction, is certainly 

 curious. II. palliata Say, with whorls convex above, and an 

 obsoletely angulated periphery, has a variety with flattened, 

 sub-exserted whorls, and carinated periphery. The same dif- 

 ferences exist between II. Carolincnsis Lea and II obstricta 

 Say, and although in a less degree in forms of H. appressa Say. 

 There is also the same relation between S. hirsuta Say and H 

 spinosa Lea, and I may add between H. Troostiana Lea and 

 Il.fastigans L. W. Sa3^ 



In the species without teeth there appears to be less tendency 

 to carination, — but H. Cumberlajidiana Lea ha§ the same rela- 

 tion to 11. alternata Say as H. obstricta to H. lyalliata. There 

 is also a carinated variety of II. intertexta Binney. 



It is worthy of remark that the strice in H. alternata and H.pal- 

 liata are replaced by costce in H. Cuinberlandiana and obstricta. 



The geographical distribution of the carinated forms above 

 mentioned is interesting. None are found in the Eastern or 

 Middle States ; they inhabit chiefly Kentucky, Tennessee, Ala- 

 bama, and Georgia, — Tennessee being their metropolis. 



Darwin (Origin of Species, p. 143, Amer, Ed.) states the fol- 

 lowing propositions, — " distinct species present analogous varia- 

 tions ; and a variety of one species often assumes some of the 

 charactei's of an allied species, or reverts to some of the cha- 

 racters of an early progenitor," He gives as a case of analo- 

 gous variation in the vegetable kingdom, the enlarged stems of 

 the common turnip, Swedish turnip, and Rutabaga, remarking 

 that, " according to the ordinary view of each species having 

 been independently created, we should have to attribute this 

 similarity in the enlarged stems of these three plants, not to the 

 vera causaoi community of descent, and a consequent tendency 

 to vary in a like manner, but to three separate yet closely 

 related acts of creation." I certainly am not prepared to accept 

 community of descent as the cause of analogous variation in 

 the American Helices above mentioned. 



