374 GEOGR.\PHICAL DISTRIBUTION. 



Diphyes fowleri, Diphyopsis mitra, and the genera Anthophysa, Angelopsis, 

 Salacia, and Porpema. (The Bathyphysinae may be left out of consideration 

 because of their mesoplanktonic habitat and because so httle is known about 

 them). These are all such large and conspicuous animals that it is not likely 

 that they would be overlooked in the intensive collecting carried on at Naples, 

 and in the Adriatic. 



It is likewise significant that none of the common and well-known Tropical 

 Atlantic species : — e. g., Abylopsis eschscholtzii, Diphyes serrata, Diphyopsis dispar, 

 Cuboides vitreus, or even the oceanic Agalma okeni, was taken by the "Research" 

 in the Bay of Biscay. 



These facts show that the faunal division drawn by Chun was an actual 

 one, and not based on incomplete observations. And when they are taken in 

 connection with the Indo-Pacific records, and the considerable amount of data 

 from the east coast of the United States, from the Bay of Biscay, from the 

 northern European coasts, and from various scattered localities in the north 

 Atlantic, they show that the Siphonophores of warmer waters are separable 

 geographically into two chief groups. The members of the first are found in 

 tropical regions of all great oceans, either on the surface or at intermediate 

 depths, or both, and are characteristic of the epiplankton of the Mediterranean. 

 In this sea, some of them are strictly seasonal, appearing only in the cooler 

 months of autumn, winter or early spring, for example Stephanomia rubra, 

 Physophora, and Praya, while Forskalia and Muggiaea are common throughout 

 the year. Several of them, likewise, are regularly found on the American coast 

 as far north as the influence of the Gulf Stream is felt (e. g. Agahna elegans, 

 Narragansett Bay), and others, as for example Diphyes subiilis, Hippopodius 

 hippopus, and Rosacea plicata, in the cooler waters of the Bay of Biscay (Bigelow, 

 :11b). As examples of this group I may mention Sphaeronectes truncata, 

 Abylopsis tetragona, Geleolaria quadrivalvis, Praya cymbiformis, Hippopodius 

 hippopus, Agalma elegans, Stephanomia bijuga, Stephanomia rubra, the genus 

 Forskalia, Rhizophysa filiformis, Porpita and Velella velella. The species of the 

 second group are exclusively tropical in their normal habitat : — they have been 

 unable to establish themselves in the Mediterranean. There are also a few 

 species which are so far known only from the Atlantic, from the Indian Ocean, 

 or from the Pacific, but it is not unlikely that their range may be found to 

 extend to the other oceans. And of course some have been recorded so seldom 

 that their position in the distributional series is doubtful. 



The factor which limits the areas of distribution of the two groups is no doubt 



