- 64 - 



The Galapagos form mentioned above, I. pontonia Dall (1) is 

 larger and has a more excavated postero-dorsal margin and more 



(1). Proc. J. S. Kat. Mus., vol. 12, p. 257, pi. 17), fiPS. 5, 

 5h, 1889. 



oonve:- base. 



Ocourrence . - laver Iliocene : Bov/den beds, Bowden, Jamaica, 



