278 



4 



Fig. 108 

 from near the surface (left) 



and near the Iwttoni (right) at 



1. Comparison of series of shell 

 Crockett. X lY^- 



2. Typical shell from near surface at Crockett. X 10. 



3. Typical shell from near bottom at Crockett. X 10. 



4. Series of shells from Crockett of progressively greater age from left to right, showing 

 in relative position of auricle through resorption of its dorsal edge with growth. X 4. 



change 



