232 PROCEEDIXGS OF THE ACADEMY OF [MaV, 



much more unfavorable than those influencing the more eastern 

 assemblages during Lignitic time.^'' 



Athleta petrosa. 



Lower Claiborne Races. 



In the Alabama sections we find forms representing in a general way 

 the Athleta petrosa main stock at a date as early as the Nanafalia 

 Lignitic. In the western Gulf region no such normal types are known 

 to the author from below the horizon of the Lower Claiborne beds. 

 In other words the Lignitic forms from Texas, etc., are (as far as ob- 

 served) abnormal, and even these senile representatives are rare. No 

 evidence of the presence of these abnormal members has yet been 

 presented by the sediments found above the Lignitic beds of this 

 region. 



The Lower Claiborne races of Athleta petrosa, then, may all be grouped 

 as members of the Athleta petrosa main stock. As a rule each locality 

 is characterized by a single, comparatively homogeneous race, the 

 great majority of whose individuals differs more or less in certain 

 minor characters from the races of other localities. Exceptionally, 

 however, we find two very slightly different strains in the assemblage 

 from a given place. These insignificant peculiarities may sometimes, 

 be important in locating the probable ancestry of later forms. iVgain, 

 in a few places we find a well-defined race of Athleta petrosa accom- 

 panied by a very closely allied derived form, which has departed 

 enough from its parent stock to be described as a distinct species. 



The Lower Claiborne of Ijouisiana and Texas furnishes many good 

 collecting grounds which afford excellent material for exhibiting the 

 variations and mutations of Athleta petrosa. Nine localities which 

 offer large series of well-preserved specimens have been selected, antl 

 the developmental shell stages of their races have been arranged in 

 tabulated form. With the exception of Moseley Feny all the localities 

 chosen have comparatively homogeneous races of Athleta petrosa. At 

 iMoseley Ferry there are, howfever, two well-marked strains of Athleta 

 petrosa. These two strains are very close, but one is of interest as 

 foreshadowing the characters of the Jackson and Montgomery races of • 

 later time. It is greatly to be regretted that our knowledge of the 

 stratigraphy will not permit us to arrange the Lower Claiborne races 

 in chronologic order. 



'" The Sabinetown beds have usually been correlated with the Wood's Bluff 

 beds of Alabama. See Gilbert D. Harris and A. C. 'S'eatch, Geol. Surv. La., Rep. 

 V, 1899, p. 67, and also A. C. Veatcli, Geol. Surv. La., 1902, p. 125. 



