- 60 - 



elongate, and has a more recurved rostrum and a more constantly 

 fine coneentrio sculpture than acuta , as that s-oecies is accepted; 

 in addition the rostral carina is sharper and the sulci more pro- 

 nounced than in the case of most a out a . Hone of the forms at hand 

 have a sculpture as coarse as that which is commonly seen in any 

 collection of acuta . The Bowden species varies -orincipallj with 

 regard to shape; while the most notable variation of acuta con- 

 cerns the sculpture. The tendency of indlp-ena toward a less 

 elongate, higher shape is very noticeable and therein lies, 

 perhaps, the prirjc ipal distinction between the two. 



I. do dona Pall (1) , of the Chipola marl of Florida, belongs 

 to the same general group. It may be distinguished by its very 

 coarse concentric rugae and also by its almost smooth escutcheon. 

 A species from the Oak Grove send of Florida, I. troohilia Dall (2) 

 is also closely related, but is recognized b^ the wide spaces be- 

 tween the often discontinuous and irregular rugae and by the ab- 

 sence of rugae on the rostral csrina. The Eocene (V/ilcox) I. rob- 

 ust a Aldrieh iZ) has coarse concentric sculpture v/aich is evenly 



(1). Trans. V/agner Free Inst. Sci., Philadel-ohia, vol. 3, pt. 

 4. pp. 589-590, pi. S2, fig. 6, 1898. 



(2). Idem, p. 590, pi. 32, figs. 4, 12, 1898. 



(3). Bull. Amer. Pal., vol. 1, no. 2, p. 17, nl. 5, fiers. 1, la, 

 l§95. 



