160 



PROCEEDINGS OF THE ACADEMY OF 



[March, 



deeply amber-colored, with the apical whorls darker, reddish-orange. 

 Whorls 3^, the last deeply descending, somewhat flattened above, 

 very convex basally, having thus a more sack-like contour than S. 

 retusa; this being its chief peculiarity. The sculpture consists of rather 

 coarse wrinkles and often some indistinct spiral impressions on the 

 last whorl. The aperture is symmetrically ovate, the columella con- 

 cave throughout, with a delicate fold above. Large specimens from 

 San Marcos measure: 



Length 16.8, diam. 9, length of aperture 11.5, width 6.7 mm. 



Length 16, diam. 8, length of aperture 10.5, width 6 mm. 



The mantle is intensely black, dappled throughout in the last whorl 

 with rounded yellowish spots. Those above the kidney are brighter, 

 more conspicuous and usually larger, often more or less confluent. 



Fig. 11. 



Fig. 12. 



Towards the edge of the mantle the spots are large and lengthened. 

 The foot including head and eye-stalks is pale grayish-white, speckled 

 with irregular grayish-black spots. The sole is pale yellow. Figs. 

 11 and 12 were drawn from specimens taken at San Marcos, Texas, 

 near the river. 



SpecimeiLS from the Rio Grande and Devil's river are of almost as 

 large size; but in some situations it is much smaller, a set from along 

 the San FiUpe river at Del Rio measuring, length 12, diam. 6.7, length 

 of aperture 8 mm. Those taken at San Antonio and New Braunfels 

 are also of small size. Such variation in size is apparently not racial, 

 but dependent upon local conditions of the food supply, etc. The 

 color and markings of the mantle are substantially the same in all 

 colonies we found, though there is individual variation in the size of 

 the light spots, figure 12 representing one of the darker individuals. 



