On the Defor)iiities of some Tennessee Helices. 157 



the umbilical region, and various distortions, roughenings, and plica- 

 tions of the surface, resulting from fracture and repairs. In all these 

 various cases the adult deformities have added the parietal tooth, the 

 lamella to the peristome, and the widely reflected lip of the species. It 

 now remains to discuss the causes of these injuries, and the probabil- 

 ity of their genetic perpetuation. A talus of loose rocks, situated upon 

 a declivity, is more or less coustantl}^ moving. If it h^s any period of 

 comparative quiet, it is during the summer or dry season of the year. 

 At all times there is more or less liability to damage, threatening the 

 moUuscan denizens of these protean retreats by the dropping of de- 

 tached masses from the overhanging cliffs; and these masses are more 

 apt to be detached during the wet season of the year, and especially in 

 spring, after the freezing and thawing of winter, than at an}^ other 

 period. But this is precisely the time, also, when these creatures are 

 most active, and have come from the deeper portions of the talus, a 

 region of comparative safety, and are crawling over its surface. 



In spring and winter, also, there is a sliding and moving of the 

 whole mass by reason of the freezing and thawing, during the progress 

 of which many of the shells are crushed and otherwise damaged. If, 

 then, 33^ per cent, of specimens taken at random are so variously de- 

 formed, we may, perhaps, rightly infer that a long continuance and re- 

 petition of injm-ies of a like character, through many generations, 

 would give rise to abnormal varieties. While accidental morphological 

 characteristics are not likely to be perpetuated; and while general an- 

 alogy stands in the way of the suggestion, the character of hermaphro- 

 ditism, and the mutual fecundation of individuals abnormally alike, may 

 present to such as choose to investigate this subject further, a key to 

 some of the m^'sterious characteristics of this mountain molluscan 

 fauna. At all events, we have numbers of specimens, entirely unin- 

 jured, exhibiting slight modifications of some of the characteristic de- 

 formities described above, and the constant repetition of accident ren- 

 ders the likelihood that its results will be persistently reproduced much 

 more probable than in the accidental cases of deformity which we ob- 

 serve under ordinary circumstances. 



Specimens are found with the spire very much elevated, the sutures 

 abnormally impressed, and the general outline very different from 

 that of the species in its ordinary form. Others are much flattened, 

 more carinate on the body-whorl, and equally far removed from the 

 ty^Qs of the species. Beside, it is in these regions that we meet with 

 the widest variation from the normal type, in many species, beside 

 the one now under discussion. Here occur the carinate and flattened 

 species of Stenotrema, the heavily ribbed and carinate species oi Pa- 

 tula, and the only sharpl}' carinate Triodopsfs. 



