MAYER: MEDUSAE FROM THE TORTUGAS, FLORIDA. 19 



Glossocodon tenuirostris, and Dyscannota gemmifera. In addition to 

 these there are a few Acalephs such as Stomolophus meleagris that are 

 strictly subtropical, having been found neither at the Tortugas nor 

 upon the southern coast of New England, but which are abundant 

 at Charleston. 



It is important to observe, also, that the Acalephiau fauna of the 

 Bermudas, like that of Charleston, is distinctly intermediate between 

 the fauna of the Tortugas and that of the southern coast of iS^ew 

 England. Of the 30 species described from the Bermuda Islands by 

 Fewkes (1883; Bull. Mus. Comp. Zool. at Harvard Coll., Vol. XL), 

 9 are established at Xewport, Rhode Island; and 16 at the Tortugas. 



I^ot a single species of acaleph known from the Tortugas has been 

 found established upon the eastern coast of New England north of 

 Cape Cod. The fauna of the eastern coast of New England is, however, 

 closely related to that of the northern coast of Europe (see Browne, 

 1895, Trans. Liverpool Biol. Soc, 96; Proc. Zool. Soc, Loudon; Hart- 

 laub, 1897; Helgolands Medusen, etc.). 



To summarize, then, we have at the Tortugas a tropical fauna that 

 gradually disappears, and is replaced by other forms, as we go north- 

 ward along the coast of the United States. Only three species of the 

 Tortugas fauna are established upon the southern coast of New England, 

 and not one extends north of Cape Cod, Massachusetts. It appears that 

 the great majority of the forms established at the Tortugas are incapable 

 of surviving in the colder waters of the north, although individuals are 

 annually driven far to the northward of their natural habitat by the 

 agency of the Gulf Stream, and the prevailing S.-S.W. winds of the 

 summer season. 



Comparison op the Tortugas Fauna with that op the Tropical 



Atlantic. 



Very instructive facts are brought to light when we compare the 

 Acalephian fauna of the Tortugas with that of the warm zone of the 

 Atlantic Ocean. By the term "warm zone" we include all that region 

 of the Atlantic lying between 30° N. Lat. and 10° S. Lat., and extend- 

 ing from the coast of Africa to the American shores. This " warm zone " 

 includes the Canary and Cape Verde Islands, the Bahamas and West 

 Indies, the Guinea Stream, the North and South Equatorial Currents, 

 and the warmer parts of the Gulf Stream. At the present time about 

 130 species of Hydromedusae are known to inhabit this "warm zone." 



