THE NAUTILUS. 39 



The apical sculpture begins with the earliest formation of the 

 shell covering and, so far as I have observed, does not extend 

 beyond the embryonic portion. Usually, at first, it consists of 

 irregular wrinkles, which are, often, quite regularly transverse 

 in position. After about the first half of the apical whorl, these 

 develop into small punctations and become regularly spiral in 

 arrangement. In some species these spiral lines of punctations 

 extend back to the very tip of the shell. In the next stage of 

 development, these rows of spiral pits become fused into a con- 

 tinuous, more or less, perfect groove and the divisions between 

 them become fine, spiral lirse. The tendency to become lirate 

 is stronger on the lower part of the apical whorl and, perhaps, 

 the most usual form of sculpture is punctate-lirate above and 

 lirate below. But not unfrequently the lirate sculpture covers 

 the whole of the last half of the whorl. 



With the exception of the species with a planorbiform apex, 

 I have not been able, as yet, to discover any sufficient differences 

 in the apical characters that would serve to differentiate the 

 characteristic species of the Alabama drainage, having a flat- 

 tened, very heavily calloused columella, from those of the Ohio 

 system with a relatively thin, rounded columellar lip. 



In the following species I have not been able to ascertain the 

 apical characters on account of the eroded condition of all of the 

 specimens on hand: S. aldrichi, biangulatus, cotistrictus, crassus, 

 pitmilux, pygmxus, tennesseensis and umbilicatus. 



The following notes give briefly the results of my examina- 

 tion of the rest of the described species: 



S. amnicoloides Walker. Apex blunt, flatly rounded. Apical 

 whorl scarcely at all everted, not constricted by the suture, 

 which is well impressed, but vertical. Sculpture practically 

 obsolete under 100 diameters. 



S. aureus Tryon. Apex prominent. Apical whorl everted, 

 sometimes very much so, convex, constricted by a deep suture, 

 which varies as the whorl is more or less everted. Sculptured, 

 at first, with strong, irregular wrinkles, then regularly, spirally 

 punctate, becoming obsoletely lirate on the second half of the 

 whorl. The tendency to liration is stronger on the lower part of 

 the whorl towards the suture. 



