228 THE MEDUSAE. 



line fauna of the Fiji Islands and that of the Tortugas. In part his state- 

 ment requires revision, as the claim to similarity is largely based on 

 correspondence of genera ; a correspondence mainly explicable on grounds 

 of the close agreement between the physical features of these two groups 

 of coral islands. But although the resemblance when analyzed proves to be 

 less close than Mayer supposed, the fact remains that there are found in the 

 Fiji Islands two species, Halitiara formosa and Pandea violacca, common in the 

 West Indies but known neither from the Indian Ocean nor from the Pacific, 

 until the capture of the latter species by the " Albatross " at Acapulco. 



The affinity between the littoral faunae of the two sides of Central 

 America is much closer in the case of the Medusae, and probably of the 

 hydroids also (S. F. Clarke, '94, : 07), of which group several species occur 

 both in the Gulf of Panama and in the Carribean, than in the higher groups 

 of animals such as ecliinoderms and fishes, in which the parallelism, at first 

 supposed to be one of species, has since been shown to be chiefly one of 

 genera only (Verrill, '67; Agassiz, : 04 ; Jordan, : 08). 



The facts of distribution disclosed by the " Albatross " expedition of 

 1904-1905 suggest that the Pacific, so far as its littoral Medusa fauna is 

 concerned, is separable into two more or less clearly defined areas ; its west- 

 ern half being closely connected to, if indeed at all separable from, the 

 Malaysian region, a fact already known to be true for echinoderras, crusta- 

 ceans (Ortmann), and for stony corals (Verrill, Vaughan) ; and its eastern 

 shores on the other hand having a close affinity to the Gulf of Mexico and 

 to the Tropical Atlantic. It would appear that although these two areas 

 undoubtedly overlap, the broad oceanic belt separating the west coast of 

 America on the one hand from Polynesia and the Hawaiian Islands on the 

 other, has proved an effective barrier to the dispersal of many of the hydroid 

 Medusae. 



Bathtmetric Range. 



The work of the recent deep-sea expeditions, American and European, 

 has demonstrated that a considerable series of Medusae, both craspedote 

 and acraspedote, undoubtedly belong to the intermediate depths. These 

 species are often termed "deep sea," " Tiefsee," especially by the Ger- 

 man investigators ; but since this term is ambiguous from its common 

 application to abyssal bottom animals, I prefer to adopt for such Medusae, 

 as well as for other organisms of similar bathymetric occurrence, the term 

 " intermediate." 



