1906.] NATURAL SCIENCES OF PHILADELPHIA. 65 



author. It cannot, however, be lower than that of the Bell's Landing 

 marl. If it is at the same horizon, we have an example of a slightly 

 senile race (the Bell's Landing) living at the same period of time not 

 far from a race (the Yellow Bluff) which exhibits, on the whole, main 

 stock characteristics. If, on the other hand, the Yellow Bluff race 

 occupies a position above the Bell's Landing marl, we have a primitive 

 race overlying a more specialized race. If this latter is the case, a 

 discordance between the geological and phylogentic successions has 

 been produced by the migration into the section of the Yellow Bluff 

 race. 



Volutilithes petrosus Conrad. 



Lower Claiborne Horizon, Claiborne, Ala. 



Very poorly preserved specimens are found in these beds. They 

 are determinable as representatives of the V. petrosus main stock, but 

 a detailed study, whorl for whorl, is not practical. 



Volutilithes petrosus Conrad. 



Claiborne Race. 



Locality — Claiborne, Ala. 



Whorls 1, 2, 3 — Smooth and rounded. 



Whorl 4 — Early in four the curved rib stage appears. It is not well 

 marked, persisting for but a short time, and is soon followed by the 

 straight, tubercled ribs of the cancellated stage. The shoulder angle 

 soon develops. The suture and shoulder tubercles are of about the 

 same size. 



Wliorl 5 — Characterized by the cancellated stage and much as in 

 the latter part of four. Spirals not strong. Suture tubercle weakens, 

 shoulder tubercle becomes stronger. 



Whorl 6 — Characterized by the cancellated stage. The suture 

 tubercle and the ribbing above the shoulder are almost gone. Shoul- 

 der tubercle stronger. Ribbing below shoulder is weaker. 



Whorl 7 — The ribbing and the suture tubercles disappear, and the 

 shoulder tubercles develop into spines during this whorl. In other 

 words, we have the transition from the cancellated to the spiny stage. 



W^iorls 8, 9, 10— All characterized by the spiny stage, but individual 

 variation is great. Senile features do not appear. 



Remarks. — Occurs in the Claiborne Fossiliferous Sand. This race 

 exhibits in general the characters of the V. petrosus main stock, though 

 it is probably not the most typical expression of that stock as it existed 

 at the time of the Claiborne deposits. The most notable features are 

 the shortening of the curved rib stage and the acceleration of the spiny 



