27 



undercurrent ; witli this novel means of ti"ans})ort they 

 passed finally to their new position, when the proper 

 conditions of light, heat, etc., arising, the eggs were 

 hatched out ! It is well known by naturalists, that the 

 ova of some land and aquatic moll asks will sometimes 

 lie dormant for years, unless the conditions for their 

 development are favorable. I have a theory of my own 

 to offer in regard to the presence of the species noted. 

 The countrj^ now covered by the city of Ciiicago, was 

 formerly low and marshy, and frequently overflowed 

 from the lake, or streams near by, and sometimes by 

 freshets. By means of these, the germs of molluscous 

 life may have been deposited. However, I regard the 

 view of Dr. Lewis as likely to be tlie true one in this 

 case ; and I understand that similar instances have 

 occured elsewhere. The Physas are remarkable for 

 their endnrance of cold, and may be seen moving 

 about at a time when other aquatic species an; torpid 

 or have buried themselves in the mud. 



i»iiy!«:i ;:ryrinn, S.VY. Sliell obloug, of a polishcd, 

 shining appearance; color light yellowish ; whirls five, 

 suture marked ; apex acute ; aperture moni than half 

 the length of the shell ; labrum slightly thickened on 

 inner margin and tinged with a reddish line ; length 16 

 mill. A fine and abundant species. 



i»Bivs.v iiin>Ki:riii.i.\A, t.ka. 



This species is placed by Mr. W. G. Binnc^y, in the 

 synonomy of P. gyrina, Say ; but I think they are 

 distinct. The following describes my specimens which 

 are large and well developed. I obtained them from a 



