1>26 THE MEDUSAE. 



it affords to the theory, urged particularly by Chun and by Vanhoffen, of 

 the unity of the holoplanktonic fauna in the warmer regions of all oceans. 

 Thus, in part through new records and in part as the result of fresh identifi- 

 cation of long known forms made possible by better material, the ranges of 

 Rhopahnema velatum, Aglaura hemistoma, Liriope tetraphylla, Solmundella bitenta- 

 culuta, Cunoctaniha octonaria, and Eirene viridula are extended to the Eastern 

 Pacific ; and since all of these were previously known from both the Atlantic 

 and the Indian oceans, their occurrence in the tropical regions of all oceans is 

 now demonstrated. Equally extended are the geographic ranges of Geryonia 

 proboscidalis, and probably of Peyantha triloba and Solmissus incisa, while Nau- 

 sithoc punctata, found in Arctic as well as temperate and tropical waters, is 

 even more widely dispersed. Solmissus marshalli may eventually prove to 

 belong to the Atlantic as well as to the Pacific when its specific relation- 

 ship to its close Mediterranean ally S. albescens is better understood. Pe- 

 gantha martagon is so far known only from the Pacific and Indian oceans 

 and from the China Sea; but it is not unlikely that its range may be fur- 

 ther extended. As to the ranges of the four new species of Narcomedusae, 

 which may naturally be expected to be widely dispersed, nothing can be 

 said as yet. 



The ranges of the following intermediate forms are likewise extended 

 to the Pacific: — Periphylkpsis braueri, Aeginura grimaldii, Crossota brunnea, 

 Homoeonema alba, Halicreas papillosum, Colobonema sericeum, Rhopahnema fune- 

 rarium, and Nausitho'e rubra. Atolla ivyrillii has not previously been recorded 

 under this name from this region ; but at least one of the Pacific records of 

 A. alexandri belong to this species (p. 39). 



Many of the intermediate Medusae are much more widely distributed 

 than most of the surface forms, PeripJu/lla, Crossota, and Homoeonema extend- 

 ing from the tropics to the Arctic (or Antarctic) regions in all oceans. This 

 phenomenon is no doubt correlated with the freedom of the intermediate 

 zone from the violent changes in temperature which limit the migration of 

 the great majority of surface animals. Thus the temperature range at 300 

 fathoms in all oceanic areas is much smaller than that occupied by certain 

 holoplanktonic surface Medusae, for example, lihopalonema velatum and Liriope 

 tetraphylla, both of which were found in temperatures of from 64° to 82° on 

 the present Expedition. 



Although the tendency of modern study is to show that the great majority 



