70 COOKE : PURPURA COROXATA, LAM. IN THE WEST INDIES. 



massive, spire more elevated, tubercles faintly marked, and in 

 some cases evanescent, the whole shell not presenting, except 

 at the extreme apex, that curiously waxen appearance which is 

 so characteristic of the type. On the other hand, the curiously 

 ribbed suture and peculiar umbilicus are well marked. The 

 shell presents the general appearance of a form occurring on a 

 muddy foreshore, which is, I believe, its actual habitat. It 

 occurs in company with P. floridana Conr., and Littorina 

 coliimcUaris Orb. The specimens from Trinidad are in all 

 respects typical. 



It is a singular fact that a shell of the size and abundance 

 of P. coronata should not have been hitherto noticed from this 

 locality, and it is quite possible that the species has not long 

 established itself on the coast, in which case it will be interesting 

 to trace the time and area of its eventual extension. The type 

 has been hitherto exclusively characteristic of western tropical 

 Africa, but the north and south range of the species does not 

 appear to have been ascertained with accuracy. 



Into the interesting question of the relation of the E. 

 American and \\\ .African tropical fauna, which is significantly 

 hinted at in the occurrence of this species on both sides of the 

 Atlantic, I do not now propose to enter. It is well known that 

 the larva of a certain Purpura is pelagic (in which form, indeed, it 

 has been more than once described as a new genus), and there 

 can be little doubt that the larval form of the species in question 

 has been carried across the Atlantic by the equatorial current 

 which sets westward from Cape Palmas. 



In the list of St. Helena mollusca, given by Mr. Edgar 

 Smith in P.Z.S., i8go, p. 250, out of 177 species, 42, or about 

 24 per cent, also occur in the West Indies. Scarcely more than 

 half-a-dozen of these, however, appear to be littoral species. 



