MAYER: MEDUSAE FROM THE TORTUGAS, FLORIDA. 25 



that of the Canaries. It should be borne in mind, however, that the 

 physical conditions in the Fiji Islands are in many respects quite similar 

 to those of the Tortugas, and are very different from those of the 

 Canary Islands. In both the Fiji and Tortugas Islands we find luxu- 

 riant coral reefs and wide areas both of deep and shallow water, 

 and in addition the temperature of the water in the two groups of 

 islands is very ueai'ly the same. In the Canaries, however, we find few 

 corals, and no extensive shallow areas, the islands being surrounded by 

 water of great depth. The temperature of the water there is also much 

 lower than at the Fiji and Tortugas Islands. 



We have shown that the Tortugas medusae cannot survive in cold 

 water, for not a single species is to be found upon the coast of New 

 England north of Cape Cod. The Tortugas forms that are now 

 established at the Fiji Islands must therefore have passed from the 

 Atlantic into the Pacific Ocean somewhere within the tropical, or 

 warm, regions of the Earth, and there can be but little doubt that the 

 Tropical Atlantic was at one time in direct connection with the Pacific. 

 Under these circumstances the Great Equatorial Current would pour 

 from the Atlantic into the Pacific, and the pelagic life of the tropical 

 regions of both oceans would become closely related. A fuller discussion 

 of this subject, and of the researches of Hill, 1898 (Bull. Mus. Comp. 

 Zool., Vol. 28) upon the geological history of the Isthmus of Panama 

 will be found in our paper upon Fiji Acalephs in 1899. 



In view of the close relationship that exists between the Acalephian 

 faunae of the Fiji and Tortugas Islands, one would be led to expect 

 that the medusae of the Gulf of Panama and the west coast of Mexico 

 would also display a resemblance to those of the West Indies and 

 Tropical Atlantic ; and this is, indeed, the case. Maas, 1897, in his 

 report upon the medusje of the "Albatross" expedition of 1891, records 

 18 species of Hj^dro- and Scypho- medusa belonging to 15 genera. All 

 but one of the genera (Chiarella) are represented in the Atlantic by 

 well-known species. Five of the Hydroraedusae from the Gulf of 

 Panama and Galapagos Islands are represented in the Atlantic by 

 species so closely related to them that, were they found existing side by 

 side in the same region, they would probably be considered to be 

 varieties one of the other. Thus : — 



Stomotoca divisa, Maas 

 Homceonema typicum, Maas 

 Aglaura prisiuatica, Maas 

 Liriope rosacea, Eschscholtz 



f S. pterophylla, of the Bahamas. 

 is very I r ./ > 



, , I IF. militare, of the Atlantic, 

 closely . , . „ . . , . 



, ^ 1 ■{ A. nemistoma, of tlie Atlantic, 

 related \ ^ .,..,,.,. 



L. ccrasiiormis, of the Atlantic, 

 to ' 



Geryonia hexaphylla, Brandt J [ G. (Carmerina) hastata, Mediterranean. 



