62 PROCEEDINGS OF THE ACADEMY OF [March, 



Whorl 8 — Still characterized by the cancellated stage, but the suture 

 tubercles and the ribbing above the shoulder have now gone. Shoul- 

 der tubercles are stronger. Ribbing below the shoulder is weaker. 

 The beginning of the tendency to form a shelly overgrowth is seen, 

 and the cancellated stage comes to an end. 



Whorl 9 — Ribbing is about gone and the shoulder tubercles have 

 become spines. In other words, the spiny stage has set in. In most 

 individuals, however, the senile characters are also mingled with those 

 of the spiny stage. The shell gets thicker, and the mantle protrudes 

 in the region of the anal siphon, and smooths the preceding whorl with 

 a shelly overgrowth. This latter, though not extreme, often covers 

 the spines of eight, which, however, are visible through it. 



Whorls 10, 11, 12 — In these whorls we simply have an exaggeration 

 of the characters of nine. The features of the spiny stage and the 

 marks of senility are found together in the same whorl. Toward the 

 end senile characters are quite well marked. The shell becomes 

 thick, the growth lines irregular, the anal siphon encroaches upward, 

 and the shoulder spines tend to pass into a shoulder keel. In addition, 

 the shelly overgrowth produced by the protruded mantle is well 

 marked, and in some specimens may be quite thick. As a rule, how- 

 ever, the spines of the preceding whorl can be counted through the 

 shelly envelope. 



Remarks. — ^This race occurs in the Bell's Landing marl. Though 

 occasionally a rare specimen may nearly approach the V. petrosus 

 main stock in its general features, the vast majority of individuals 

 show such a development of senile characters that it is necessary to 

 consider the race to be a senile offshoot from the main stem. These 

 senile marks though typical are not highly developed. This race 

 unquestionably sprang from the senile individuals which occurred as a 

 minority in the otherwise normal, geologically earlier Gregg's Landing 

 race. 



Volutilithes petrosus Conrad. 



Wood's Bluff Race. 



Locality — ^Wood's Bluff, Tombigbee River, Ala. 



Whorls 1, 2, 3 — Smooth and rounded. 



Whorl 4 — The curved rib stage appears early in four and persists 

 for about a quarter of a whorl. It is followed by the straight, tubercled 

 ribs of the cancellated stage. The suture and shoulder tubercles are 

 about equal in size. A shoulder angle soon develops. The tubercles 

 are connected by spirals. 



