GEOGRAPHICAL DISTRIBUTION. 369 



zone where wave action is violent. Agalmids and For.skalias are such feeble 

 and erratic swimmers that it can hardly be supposed that they can transport 

 themselves to a more placid environment as the result of tactile stimulus. A 

 Forskalia caught on the surface by a breaking sea, is likely to suffer the same 

 fate that befalls a large and unwieldy Aurelia or Cyanea when o\'ertaken by the 

 same circumstances at the end of the season, i. e. to be broken to pieces. Thus 

 physical conditions in the high seas prevent their attaining the faunal promi- 

 nence in oceanic regions which they possess in the Gulf of Naples or among the 

 Canary Islands. 



Oceanic temperatures and their relation to distribution. 



We know one Siphonophore, and one only, Diphyes arctica Chun, of which 

 we can say without hesitation that it is restricted to Arctic and Subarctic regions. 

 Three other species may finally be grouped with it, Galeolaria truncata Sars, 

 G. biloba Sars, and Stephanomia cara A. Agassiz. It is true that the first of these 

 has been identified by Lens and Van Riemsdijk (:08) with a species from the 

 Canaries, G. inflata Chun (p. 235) ; but the latter is so insufficiently described 

 that the relationship is doubtful. Galeolaria biloba is indistinguishable, so far 

 as Sars's ('46) rather brief description goes, from the Indian Pacific G. australis; 

 and there is a possibility that it is likewise identical with the Mediterranean 

 "Diphyes turgida" of Gegenbaur. But to settle this question will require a 

 fresh study of the Norwegian and Mediterranean forms. Stephanomia cara is 

 certainly closely allied to S. bijuga; but if it be identical with it, it would 

 afford an anomalous case of distribution (p. 284). Arctic specimens of »S. cara, 

 as of G. biloba, must be reexamined with their specific relationships in view, 

 before the question of its standing can be settled. 



Diphyes arctica is of more than ordinary interest in its geographic relations 

 because of its temperature range. It is common at Spitzbergen (Romer); 

 in the Arctic Ocean north of Russia (International committee lists), in the 

 Greenland Sea both at the surface and at considerable depths (Damas and 

 Koefoed) ; and along the coast of Norway to the Skagerak, where it is known 

 from intermediate hauls only, the shallowest being 200 meters. On the Nor- 

 wegian coast it occurs only accidentally, if at all, on the surface, but is a common 

 constituent of the mesoplankton. Its records from the "Plankton" expedition 

 are from 59° 20' N., 11° 8' W., and 60° 30' N., 27° 0' W., between 400 meters and 

 the surface. Damas and Koefoed (:07) recenth' discussed the distribution of 

 this species at some length. I agree with their conclusion that its occurrence 



