114 THE NAUTILUS. 



than any of the Florence series, and the body whorl ia much more 

 gibbous. This feature is still more emphasized in a small series of 

 prcerosa from the Ohio at Golconda, Ills., also collected by Mr. 

 Hinkley. In these (Fig. 6), as the shell advances beyond the 

 bicarinate stage, the lip passes over the superior carina and overlaps 

 the preceding whorl, forming a slight shoulder around it, so that 

 upon the completion of an entire whorl, the spire appears, as it were, 

 in a flattened depression with the short, apical elevation in the 

 centre. Whether this is constant in the prcerosa of the Ohio, the 

 series under examination is too small to establish. But the simi- 

 larity of the specimen from the Falls of the Ohio (the type locality) 

 suggests that it may be. It is very desirable that a full series of all 

 sizes from the Ohio should be examined, so that the manner of 

 growth of the typical form may be definitely determined. 



By a careful selection of the less eroded specimens, the whole 

 process of growth can be traced from the typical bicarinate form of 

 the young to the smooth rotundity of the adult shell and there is 

 apparently no question but that the cincinnatiensis of Lea is the 

 young of the prcerosa of Say. 



II. ANCULOSA SUBGLOBOSA Say. 



This species, in some localities at least, seems to be less subject to 

 erosion than its associated species of the genus; and specimens nearly 

 if not quite mature, with perfect apices, are not uncommon. The 

 tracing of the growth of the shell from the early stages to maturity 

 is, therefore, a matter of comparative ease. 



The series of young shells in the Lewis collection, of which the 

 smallest (Fig. 9) measures alt. 3.25, diam. 3.55 mm., with one ex- 

 ception, is very uniform, and there can be no doubt but that they are 

 the young of the typical form as figured by Tryon (Mon. figs. 799 

 and 800). They are gibbous, translucent, light horn-color, unicol- 

 ored or banded, smooth and shining, apex acutely conical, the tip 

 tinged with dark brown, whorls rounded, suture well impressed, with 

 no trace of any carina whatever. The shell increases very rapidly 

 in size, but retains its peculiar form until nearly mature. For com- 

 parison with Figs. 3 and 8 a larger specimen (5x5 mm.) is also fig- 

 ured (Fig. 10). 



The exception above noted (Fig. 11) is quite different in shape 

 and would seem to be specifically distinct. It measures 5.5x5 mm., 



