GEOGRAPHICAL DISTRIBUTION. 367 



whether its representatives in the two are specifically distinct or identical can be 

 determined only by a fresh study of Atlantic specimens. Porpita and Velella, 

 like Physalia, are represented in the Atlantic and in the Pacific by distinct, though 

 closely allied species. But the exact relationships of the representatives of these 

 genera from the Indian Ocean are not known. In the case of Velella it is probable 

 that we can speak of an Indo-Pacific species, just as we can of Physalia. But 

 there is some, though not conclusive, evidence, that the Indian form of Porpita 

 is more closely allied to the Atlantic than to the Pacific species. 



Summarizing these results, and omitting the problematical species, and 

 those whose validity is doubtful, we find no less than forty-one valid species of 

 Siphonophores, out of a total of about 95, i. e. almost half, are already known to 

 occur both in the Atlantic and in some part of the Tropical Indo-Pacific areas; six 

 which are known only from one are represented in the other by allies so close 

 that it is doubtful whether they are distinct; twelve are so far known only from 

 the Atlantic, and sixteen from the Indo-Pacific. And judging from the rich 

 harvest brought to light by the recent deep-sea expeditions, there is every reason 

 to expect that this number common to the two great oceanic divisions will be 

 augmented by the report on the "Valdivia" Siphonophores, now in preparation 

 by Dr. Chun. 



There is no great discrepancy between Calycophores and Physophores, 

 so far as the proportion of species common to both oceans is concerned. But 

 while several of the former, as for example Abylopsis teiragona, Diphyes appen- 

 diculata, and Diphyopsis dispar are constantly met with in the warmer portions of 

 all oceans, this is the case with comparatively few Physophores, though many 

 species of them are known from' various localities in both the Atlantic and the 

 Pacific. The only Physophore encountered by the "Albatross" with anything 

 like the regularity of the commoner Calycophores was Agalma okeni, and only 

 two others, Physophora hydrostalica and Anthophysa rosea, were taken at more 

 than five stations each. The "Plankton" expedition took only four Phy- 

 sophores: — Nedalia loligo at two stations, Physophora hydrostalica, Anthophysa 

 formosa, and Athorybia rosea at one station each (Chun, '97b). In the Bay of 

 Biscay the "Research" found no Physophores at all, except one fragmentary 

 Athorybia. The Anthophysidae and Rhodaliidae as a whole seem to be rare 

 everywhere. But Forskaliidae and the long-stemmed Agalmids are common in 

 the Mediterranean, at the Canaries, among the West Indies. Agalma elegans 

 and Stephanomia cara occur regularly at various localities along the Atlantic 

 coasts of North America and of Europe, and Stephanomia bijuga swarms at times 



