194 AMERICAN JOURNAL 



Locality. — Santa Cruz, West Indies. Mus. Phil. Acad. Nat. 

 Sciences. Presented by Geo. Davidson. 



Observations. — This animal cannot be confounded with S. sepi- 

 oides, which occurs in the same waters, that species having larger 

 rhomboidal fins and a proportionately larger head and arms. 

 It is more like S. Blainvilliana from Java, but has smaller arms, 

 with a different formula, narrower fins, though of nearly the same 

 shape, and is much more acuminate at the base. 



*S'. Sloanii, the only other species reported from the West 

 Indies, is essentially different in having the shell with the margin 

 thickened, while our species has it very thin. 



