46 DAVENPORT ACADEMY OF NATURAL SCIENCES. 



With regard to the distribution of the mollusca of Florida, my expe- 

 rience has given the following results : 



First — On the west coast the marine shells consist of a number of 

 Atlantic coast forms, a few species peculiar to the south-east coast of 

 the United States, and a very large number of West Indian shells. 

 From the vicinity of Tampa Bay to the extreme point of Cape Sable, I 

 found but little change in the species. Such shells as Strombus pugilis, 

 the Fulgurs. Pyrula papyracea, the Fasciolarias, Melongena corona, 

 Xatica duplicata, Oliva literata, Nassa vibex, Littorina angulifera and 

 irrorata, and Crepidula fornicata, among the Gasteropods, and Ostrea 

 virginica, Venus mortoni, Loripes edentula, Mactra similis, Donax 

 variabilis, Cytherea gigantea, Cardium magnum, several species of 

 Mytilus and Modiola, and the Pinnas seminuda and muricata, among 

 bivalves, are characteristic of the west coast throughout the region 

 which I have indicated. A few West Indian species become more 

 plentiful as we go southward; thus, Cancellaria reticulata is somewhat 

 rare in the vicinity of Tampa Bay, but is plentiful on Sannibel Island, a 

 hundred miles south, and so on to the extreme end of the State. Tel- 

 lina piiniceus is very seldom found north of the Caloosahatchee River, 

 but at Cape Sable it is abundant; Natica canrena is more abundant to 

 the southward, etc. Still, the difference in a collection of shells made 

 at Anna Maria Key and one from Cape Sable is hardly perceptible. 

 But when one crosses over to the nearest of the lower range of Keys a 

 very different shell fauna is met with. On these Keys the character- 

 istic species are such shells as Vasum muricatum, Strombus gigas and 

 bituberculatus, the Tritons, Ricinula nodulosa, the Purples, Marginella 

 carnea and guttata, Ovulum gibbosum, Columbella mercatoria. the 

 Cypraeas, the Doliums, the Neritas, the violet snails, several species of 

 Littorina, the Imperators, a number of Acmaeas, the Strigillas, Mytilus 

 exustus, the Pernas, and the like, scarcely one of which is ever found on 

 the west coast of the mainland at all. 



This change maybe accounted for in part, no doubt, by the fact that 

 the Keys are of coral formation and that the shores of the west coast 

 of the mainland are mostly sandy; but I believe the Gulf Stream to be 

 accountable for most of this. It sweeps to the southward a long way 

 to the west of the mainland of Florida, but is crowded in close to the 

 Tortugas and the Florida Keys, and is kept in near to these Keys on 

 the south-eastern shore and for a long distance up the east coast of the 

 mainland. The theory that this is the distributor of many of these 

 tropical forms is sustained by the fact that such shells as Purpura flori- 

 dana, Strombus bituberculatus, Marginella carnea, Cassis tuberosa and 



