THE NAUTILUS. 115 



Alt. 3^, diam. 3^ mm. 



Types (No. 21944 Coll. Walker), from the Coosa River, Chilton 

 Co., Ala. Also Catawba River, Ala. Cotypes in the collection of 

 T. H. Aldrich. A single specimen of this extraordinary species was 

 detected in a set of S. georgianus from the Catawba River, in the 

 Lewis collection, when my former paper on Somatogyrus (Naut., 17, 

 p. 140), was in preparation. But it was of such unusual form that it 

 seemed more likely to be a monstrosity than a distinct species. Re- 

 cently, however, Mr. T. H. Aldrich has submitted a set from the 

 Coosa, which are remarkably uniform, and leave no doubt but that it 

 is entitled to specific recognition. The discovery by Mr. Hinkley of 

 another but very distinct carinated form in the Tennessee River 

 at nearly the same time is an interesting coincidence, and, like the 

 similar case of S. umbilicatus and strengi, affords a striking example 

 of evolution along parallel lines in two different drainage systems. 



SOMATOGYRUS PUMILUS (Conrad). PI. 5, fig. 10. 



Conrad's original description of this species is very meagre and no 

 dimensions are given. His figure subsequently published in the 

 American Journal of Conchology V, PI. 15, fig. 5, is on too small a 

 scale to be entirely satisfactory. Fortunately, however, his type has 

 been preserved in the collection of the Philadelphia Academy of 

 Natural Sciences, and until now has been the only specimen known. 

 Recently Mr. T. H. Aldrich has submitted a small form from 

 Cahatchee Creek, Shelby Co., Ala., which seemed to be very similar. 

 Dr. Pilsbry has kindly compared them with the type and writes 

 " they are not quite pumihis, as the columella is decidedly too wide 

 and calloused." A careful comparison made during a recent visit to 

 Philadelphia, however, satisfied us both that these specimens could 

 not be distinguished from Conrad's species. In the absence of topo- 

 types, it seems desirable to describe and figure the Cahatchee form for 

 comparison with the new species that have recently been described 

 from the same region. 



Shell small, sub-globular, imperforate, thick, solid, pale-green, 

 becoming somewhat yellowish towards the aperture, smooth, with 

 very fine growth-lines. Spire depressed, obtuse, whorls probably 

 3-3^ (apex eroded), those of the spire slightly convex with a well 

 impressed suture ; body-whorl large, inflated, regularly rounded. 

 Aperture subcircular, broadly angled above, regularly rounded below, 



