1906.] NATURAL SCIENCES OF PHILADELPHIA. 59 



dividual variation, yet nevertheless possessing on the average definite 

 racial characters. In other words, the majority of specimens from 

 any one locality or horizon show a certain stage of evolution. Some 

 of the specimens may show developmental features characterizing 

 either a more primitive or a less primitive race; but these specimens 

 are few, and are not typical of the average of individuals from the 

 locality or horizon to which they belong. 



The races of V. petrosus are known to range from the A^anafalia beds 

 to the Jackson beds inclusive. The original specific description '^ is 

 accompanied by a figure of a member of the Claiborne race. Though 

 this particular race is perhaps not the most typical expression of the 

 V. petrosus main stock, the writer feels that no better method can be 

 employed than to use the name V. petrosus to designate the assemblage 

 of races under discussion. 



Several of the races differ in the development of senile characters 

 from the V. petrosus main stock, but there is every gradation between 

 these and the representatives of the main stock. On account of this 

 gradation the senile forms are included as races of V. petrosus, in spite 

 of the fact that their old individuals differ greatly in appearance from 

 those of the more normal type. 



The young of all the races, senile and otherwise, are remarkably 

 uniform and constant. The early whorls indicate clearly that they 

 are all descended from a cancellated ancestor, and bear a strong re- 

 semblance, especially in the cancellated stage, to the characters of 

 V. limopsis. In the absence of any record of a V. petrosus being found 

 below the horizon of the Nanafalia beds, the author believes that it 

 is perfectly safe to conclude that all these races in question are de- 

 scended from the V. limopsis of the Matthew's Landing horizon. 

 Volutilithes petrosus Conrad. 



Nanafalia Race. 



Locality — Nanafalia, Ala. 



The only specimen known to the writer from this horizon is not suf- 

 ficiently well preserved to admit of its accurate study whorl for whorl. 

 It is, however, a perfectly normal specimen of moderate size and ex- 

 presses the general characters of the V. petrosus main stock. It is 

 about the size of the eight-whorled individuals of the Gregg's Landing 

 or the Jackson races. When it is placed in line with such specimens, 

 the three shells exhibit very few differences. This Nanafalia individual 



* Valuta petrosa Conrad, "Fossil Shells of the Tertiary Formations of North 

 America. ' ' 



