MAYER: MEDUSA FROM THE TORTUGAS, FLORIDA. 17 



both the north and south ends of the island in a westerly direction. The 

 island thus assumes, roughly, the form of a crescent with its horns 

 pointing westward. The north winds that occur during the winter 

 months annually destroy these crescentic horns, but they are annually 

 replaced by the summer breezes. 



Although the northern edge of the current of the Gulf Stream prob- 

 ably never impinges against the Tortugas, a fresh south breeze is suffi- 

 cient to drive its surface waters, unaccompanied by the current,^ upon 

 the islands, and under these conditions vast quantities of gulf-weed, 

 and large numbers of Physalia, Velella, and other pelagic animals are 

 cast up upon their shores. It is well known that the Gulf Stream 

 bears along upon its surface vast numbers of floating animals that ai'e 

 drawn into it by winds and currents from the adjacent tropical regions 

 of the Atlantic, and thus it comes about that pelagic animals from all 

 over the Gulf of Mexico and West Indies are drifted past the Tortugas. 



The temperature of the surface waters in the immediate vicinity of 

 the Tortugas is remarkably high, being about 74°-77° F. in winter, 

 and 80°-86° F. in summer, the average for the whole year being about 

 78° F. It is probably owing to this high temperature, and also to the 

 great purity of the ocean water, that marine animals may be maintained 

 alive in aquaria with remarkable success at the Tortugas ; for the tem- 

 perature of the laboratory is almost sure to be lower than that of the 

 sea, and thus the animals in the aquaria are refreshed and thrive well. 



Comparison op the Tortugas Fauna with that op the Southern 



Coast of New England. 



Ninety species of Acalephs have been found at the Tortugas. Of 

 these, 62 are Hydromedusa?, 16 Siphonophorfe, 7 Scyphomcdusa), and 

 5 Ctenophora). Of these, 39 species are new to science, 33 being 

 Hydromedusa?, 3 Siphonophorse, 1 Hydroid, and 2 Scyphomedusso. 



The Acalephian fauna of the Tortugas is strictly tropical, and is 

 totally different from that of the eastern coast of New England north 

 of Cape Cod. A number of characteristic Tortugas forms are, however, 

 blown northward every summer, and are thus found in considerable 

 numbers upon the southern coast of New England, where they have 

 been found in Newport Harbor and in Buzzard's Bay. Only three 

 Tortugas species have, however, succeeded in establishing themselves 



1 See Lieutenant (now Commander) J. E. Pillsbury, 1886, Report of U. S. Coast 

 and Geodetic Survey, Appendix No. 11, p. 287. 



