1907.] NATURAL SCIENCES OF nilLADELPHIA. 231 



stratigraphy of the minor divisions is there only poorly understood. 

 The researches of Prof. Gilbert D. Harris have, it is true, done much 

 to make clear the succession in Louisiana and Texas; but it is still 

 impossible to ascertain the relations of the less important beds with 

 each other or with their time equivalents in the standard sections of 

 Alabama. In this western Gulf region we have three well defined 

 formations in which Athleta petrosa and its allies occur. These are the 

 Lignitic, Lower Claiborne and Jackson. 



Morphology. 



As with the races from the Alabama sections, we find that the Athleta 

 petrosa assemblage from any one locality or horizon is apt to differ 

 more or less from that found at another locality or horizon. Not 

 infrequently certain individuals of a race will depart to some extent 

 from the racial norm, but these make usually but a small minority of 

 the assemblage. "In other words, the majority of specimens from 

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



Throughout the present paper the author has used the same terms 

 which were employed in dealing with the Alabama forms. As before 

 we have the smooth stage, curved rib stage, cancellated stage, spiny 

 stage and senile stage. The senile and spiny stages may be separate 

 or associated together in the same whorl. Rib, spiral, tubercle, spine, 

 etc., are all used in the same sense, and the end of the fu'st whorl is 

 again placed (arbitrarily, of course) in the same position. 

 Athleta petrosa tuomeyi. 



Sabinetowui Race. 



Locality. — Sabinetown, Texas. 



Horizon. — Lignitic beds. 



This series is small and the individuals are poorly preserved. There 

 are no very young ones, and the shelly overgrowth produced by the 

 protruded mantle is very extreme in the old individuals. This, together 

 with the poor state of preservation, renders detailed morphologic work 

 impossible. These forms are typically senile, the most marked feature 

 being the monstrous shelly overgrowth which results from the pro- 

 trusion of the mantle onto the preceding whorl. In addition they arc 

 very small and dwarfed. They resemble closely the Hatchetigbee 

 forms of Alabama, but are even more extreme and dwarfed. If they 

 are members of the same senile phylogenetic series which we find in 

 Alabama they are indeed descendants of the Hatchetigbee Bluff Race. 

 They may, however, be synchronous with any one of the Alabama 

 senile groups, and be merely the expression of conditions which were 



