64 PROCEEDINGS OF THE ACADEMY OF [Mai'Ch, 



earlier Bell's Landing race. It has unquestionably been evolved from 

 the Bell's Landing race by an exaggeration of senile characters. 

 Volutilithes petrosus Conrad. 



Hatchetigbee Bluff Race. 



Locality — Hatchetigbee Bluff, Tombigbee River, Ala. 



The series of young individuals at hand is so small, and the ghelly 

 overgrowth produced by the protruded mantle is so great in the old 

 individuals, that a detailed study of the specimens, whorl for whorl, 

 is not practical. 



These forms are extraordinarily senile, and have been derived from 

 the geologically earlier Wood's Bluff race by an exaggeration of the 

 senile features. The shoulder spines tend to pass into a shoulder 

 keel, the shell is thick, the growth lines irregular, the anal siphon 

 encroaches upward, and the preceding whorl is encumbered with the 

 shelly overgrowth. This last feature is very extreme. In addition 

 the race is, on the whole, a dwarfed race, the full-grown individuals 

 being smaller than those of the earlier less senile races. This race is 

 the end term of the senile offshoot which diverged from the V. petrosus 

 main stock in Bell's Landing time. The author knows of no authentic 

 abnormal senile specimen from beds higher than the Hatchetigbee 

 horizon in Alabama or Mississippi.^ 

 Volutilithes petrosus Conrad. 



Yellow Bluff Race. 



Locality — Yellow Bluff, Alabama River, Ala. 



Unfortunately the material at hand is not sufficiently well preserved 

 to give a detailed description, whorl for whorl. Nevertheless, there is 

 no difficulty in making out the following points. The great majority 

 of individuals possess, in general, the characters of the V. petrosus 

 main stock, and have arrived at little more than that evolutional 

 stage which is typified by the Gregg's Landing race. 



Though a few individuals exhibit senile characters, these latter are 

 only very slightly developed, and we are undoubtedly warranted in 

 placing the Yellow Bluff race on the Volutilithes petrosus main stock 

 as the descendant of the Gregg's Landing race. 



The exact stratigraphical horizon for this race is unknown to the 



'See Trans. Wag. Inst., Vol. Ill, part 1, p. 7.5. The statement made on this 

 page by Dall is not borne out by a study of full collections. He says that Athleta 

 "is foreshadowed by the distorted specimens of Volutilithes petrosa to which I 

 have already referred, and which occur from the Lower Eocene of Alabama 

 (Wood's Bluff) up to the Claiborne Sands and the beds known as Jackson, over- 

 lying the Claiborne, associated with the undistorted normal form, which is always 

 more numerous." 



