234 



PROCEEDINGS OF THE ACADEMY OF 



[May, 



AtWeta petrosa. 



Montgomery Race. 



Locality. — Montgomery, Louisiana. 



Horizon. — Jackson beds. 



The Montgomery race is, from a geological standpoint, cotemporane- 

 ous with the Jackson race of Jackson, Mississippi. In its early whorls 

 it is perhaps a little less accelerated than the Jackson race. The 

 following table will serve to illustrate its relations with the Mississippi 

 forms and with the probable Lower Claiborne ancestor. 



1 2 o 4 5 G 7 8 9 10 11 12 



Moseley Ferry (Jackson 

 Strain). 



Montgomery, La. 



Jackson, Miss. 



Table II. — Showing slight acceleration of the curved rib stage and the beginning 

 of the cancellated stage in the A. petrosa races of Jackson time. The Lower 

 Claiborne ]Moseley Ferry form is introduced as a probable ancestor. 



Athleta clayi n. s." 



Locality. — St. Maurice, Louisiana. 



Horizon. — Lower Claiborne. 



The more important morphological features of this species may be 

 summed up as follows : 



Whorl 1. — Smooth and rounded. 



Whorl 2. — Smooth and rounded at first, but soon a very few untuber- 

 cled but nearly straight ribs appear. These probably represent a 

 somewhat suppressed and condensed clu•^'ed rib stage. They are 

 followed by the straight tubercled ribs of the cancellated stage. At 

 first the suture tubercle is the larger, but a shoulder angle soon forms 

 and the shoulder tubercle becomes dominant. 



Whorls 3, 4. — Characterized by the cancellated stage. Much as in 



'' This species has been named in honor of Mr. Randolph Clay, of Philadelphia. 



