116 THE NAUTILUS. 



noticeably lighter in color than the rest of the shell and stand out 

 conspicuously against the dark bands above and below them. As 

 the shell grows, the superior band widens and invades the region of 

 the superior carina, sometimes before it has entirely disappeared, and 

 occasionally divides into two narrow bands, the basal band persists 

 and in the adult the space between them represents the intercarinal 

 area of the young shell. 



The spiral lines are uniformly present and rather stronger than in 

 cincinnatiensis and apparently persist longer as the shell approaches 

 maturity. 



As the shell increases in size, the superior carina diminishes and 

 finally disappears entirely ; the lower carina persists much longer, 

 descends somewhat in position and becomes a characteristic feature 

 of the half-grown shell and, in the adult, causes the bell-shaped form 

 which gives to the species its specific name. 



IV. Conclusions. 

 From the examination of the material as above detailed, the fol- 

 lowing conclusions may be drawn. 



1. That in these species of Anculosa at least, the very young shells 

 have characteristics which are constant and available for specific 

 distinction. 



2. That the young shell of A. prserosa is bicarinate and spirally 

 striate and was described by Lea as A. cincinnatiensis. 



3. That the young shell of A. subglobosa is ecarinate and without 

 spiral, impressed lines. 



4. That the young shell of A. tintinnabulum is bicarinate and 

 spirally striate, but specifically different from Lea's cincinnatiensis. 



5. That A. tintinnabulum Lea is specifically distinct from both A. 

 prserosa and A. subglobosa, and is a valid species. 



6. That collectors and especially those in the field should give 

 special attention to securing full suites of all the species of all ages, 

 particularly the very young, so that the exact relations of all the 

 described species may be definitely determined. 



EXPLANATION OF PLATE X. 



All the figures are on the same scale, X 48. 



Fig. 1-4. A. prserosa Say — Tennessee River, Florence, Ala. 



Fig. 5. A. prczrosa — Falls of the Ohio. 



