140 THE NAUTILUS. 



ated and more inflated above and has an entirely different form of 

 colurnellar lip. Dr. Pilsbry has kindly compared some of the Ten- 

 nessee river specimens with the unique type of Conrad's pumilus,i\i\d 

 writes that while pumiius has the same peculiar axial groove, it is 

 smaller (alt. 3.9, diam. 3 mm.), different in color and has the aperture 

 more oblique. Doherty's species is smaller, about the size of S. in- 

 teger, and has the axial groove only slightly developed. The three 

 species, however, form a natural group more closely related to each 

 other than to the other species in the genus. Many of the specimens 

 in the Lewis collection have the aperture rather more expanded 

 below than in the typical form. 



This species is apparently ovoviviparous. In four out of fifteen 

 examples in the lot from the Tennessee river, young shells of about 

 2^ whorls and about 1^ mm. in height and breadth were found lodged 

 behind the opercula of the adults in various degrees of extrusion. In 

 two cases the young shells dropped out in the cleaning process, the 

 outer edge of the operculum being forced out of its normal position 

 to allow the passage of the young. In the other two, the young are 

 further within the shell and the operculum is set in nearly its usual 

 position. An interesting monstrosity, which apparently belongs to 

 this species, occurred in the lot from the Cahawba river. Nearly the 

 whole of the body whorl is encircled at the periphery by a strong 

 carina. It appears from beneath the upper insertion of the lip and 

 continues around the whorl about three-fourths of the circumference, 

 when it rapidly subsides and entirely disappears before the lip is 

 reached. There is no trace of it on the upper whorls that remain. 

 The axial groove is bounded on the inner side by a sharp angle, which 

 merges into the edge of the lip at the base. 



Somatogyrus pennsylvanicus n. sp. PI. v, figs. 15 and 16. 



Shell small, obtusely conic, narrowly umbilicate, sometimes im- 

 perforate, light horn-color, smooth, with very fine growth-lines. Spire 

 elevated, apex obtuse. Whorls about 4^, convex, slightly flattened 

 toward the suture, which is well impressed. Aperture ovate, less 

 than half the length of the shell, angled above and rounded below, 

 slightly flattened along the basal lip. Columella nearly straight with 

 a rather heavy, but narrow, rounded callus, which is thin and trans- 

 parent in the parietal wall. Umbilicus a mere chink or entirely 

 covered by the callus deposit. Lip simple, somewhat thickened 

 within, especially on the basal part. Alt. 3|, diam. 2^ mm. 



