60 PROCEEDINGS OF THE ACADEMY OF [March, 



has spines in its last whorl which make it resemble the Jackson race 

 quite closely. In this respect it is nearer the Jackson specimens than 

 the Gregg's Landing specimens. Its mantle perhaps smooths the 

 preceding whorl a trifle more than does the mantle in the Jackson race. 

 However, in its general features, it is very close to the Jackson form. 

 The amount which the mantle has smoothed the preceding whorl is 

 about equal to that found in shells of the same size from Gregg's 

 Landing. 



Volutilitlies petrosus Conrad. 



Gregg's Landing Race. 



Locality — Gregg's Landing, Alabama River, Ala. 



Whorls 1, 2, 3 — Smooth and rounded. 



Whorl 4 — The curved rib stage begins early in four. It persists for 

 a quarter or a third of a whorl, but changes abruptly into the can- 

 cellated stage with its straight, tubercled ribs. The shoulder and 

 suture tubercles are of about the same size at first. By the end of 

 four the shoulder angle is quite well developed. 



Whorl 5 — Characterized by the cancellated stage and much like the 

 latter part of four. Suture and shoulder tubercles are of about the 

 same size. The shoulder angle is well developed. Tubercles are 

 connected by fine spirals. 



Whorl 6 — Characterized by the cancellated stage, but changes occur. 

 The shoulder tubercle is becoming stronger, while the suture tubercle 

 is getting weaker. The ribbing above the shoulder angle is also 

 becoming weaker. 



Whorl 7 — Still characterized by the cancellated stage, but here 

 the suture tul^ercle has disappeared and is only represented by its 

 spiral. The ribbing above the shoulder angle has gone, though it is 

 still well represented below the shoulder angle. 



Whorl 8 — Still characterized by the cancellated stage and much like 

 whorl seven. Below the shoulder angle the whorl is covered with fine 

 spirals. There is a very slight smoothing of the preceding whorl by 

 the protruded mantle, for the end of the cancellated stage is not sharp 

 like that of the curved rib stage. 



Whorl 9 — From here on individual variation is great. Some forms 

 have a whorl much as in eight, with the ribbing still well developed 

 below the shoulder, though the shoulder tubercles are more spine- 

 like. In other specimens the ribbing below the shoulder is gone, the 

 shoulder spines are more extreme, and the anal siphon shows a tend- 

 ency to encroach upward on the preceding whorl. In addition, these 



