212 Qiiartetiy Journal of ConcJiology. 



of the river between Wetumpka and above that place to Claiborne^, 

 the locahty of Mr. Conrad's types. Whether this indicates that 

 the T. angii/atn varies in its down-stream distribution, until it 

 reaches the enormous development of the typical T. mag)iifita is a 

 problem that I have not the proper means of determining, but 

 while there are intermediate forms, they are in no case adult ^ so far 

 as my observation extends, and as the shells are separated by bet- 

 ter and more constant characters than are often regarded as being 

 of specific value, I have deemed it proper for the present, to treat 

 them as different species. 



They are separated by the following remarkably distinct and 

 constant characters: T. viagnijica is a very massive and heavy 

 shell, attaining dimensions of 50 millimetres. T. angtilata is 

 comparatively light and thin, and seldom exceeds 30 mill. The 

 whorls of T. magnijica are heavily waved, and ornamented with 

 double rows of tubercles, while the sutural angle is abrupt, leaving 

 the top of the whorls squarely 'houldered. Those of T. angjtlata 

 are smooth, or very slightly nodulous, with a long, sloping an.ole 

 to the suture, about which there is a very small shoulder. The 

 aperture of T. magnijica is proportionally much smaller than that 

 of T. angiilata, and the row of tubercles produces abrupt, angular 

 indentat ons of the lip; while that of T. angulata is more regularly 

 curved These differences are apparent at the slightest glance, 

 and do not seem to be the result of differences of habitat, as the 

 transitional forms do not occur between the localities furnishins: 

 the typical specimens of the species: at least they do not occur as 

 adult. 



The T. Coosaensis is so \ery distinct from the other forms, as 

 to almost warrant its generic separation. The aperture is nearly 

 circular, like that of Vivipara: the shell small, perforate, and com- 

 paratively thin: the sutures are deeper: the whorls convex at base 

 and sides, but distinctly and widely planiform above. Yet the 



