CTENOPHORA. 



73 



occur even so far as the Aland Sea, according to Levander"), the species being thus evidently very 

 euryhaline, even if it is found there only in the deeper water. It is in good accordance therewith 

 that it is also stated to occur in the Black Sea (Conip. above, p. 69). By the German vSouth Polar 

 Expedition it was found in considerable numbers in the Antarctic Sea, Moser (Ctenoph. d. deutschen 

 Siidpolar-Exp. p. 144) pointing out "dass hier ein Fall von Bipolaritat vorliegt, wie er bis jetzt nur 

 bei ganz wenig Arten nachgewiesen ist". The fact recorded by Dr. Moser herself (Op. cit. p. 143) 

 that it also occurs at the Seychelles and at Ascension is, however, not in favour of regarding this as 

 a case of bipolarity; it shows that the species is also found in the warm regions, so that it will probably 

 prove to occur all over the oceans, not only in the Northern and Southern seas, its distribution thus being 

 not discontinuous, as it ought to be, if it were really a case of bipolarity. — From the Pacific this species 

 is not known with certainty. Ghigi (Op. cit. p. 9) states that it occurs at the West Coast of North 

 America down to the Californian peninsula. This statement, however, evidently rests on the suppos- 

 ition that the Phurobracliia bachci figured by Torrey (The Ctenophores of the San Diego Region, 

 PI. I, Fig. 3) is identical with Pl.pileus, a sujDposition which is also made by Moser (Op. cit. p. 145). 

 While I quite agree that Torrey's PL bachei Aiiiers from the true P/. bac/ifi Agass. in what appears 

 to be the main character of this species, viz. the opening of the adradial vessels into the meridian 

 vessels above (aborally to) the opening of the tentacle sheath, so that it can scarcely be identical with 

 this species 2), I cannot, on the other hand, accept its identity with Pl.pileus, the shape and oblique 

 direction of the tentacle bases and the position of the opening of the tentacle sheath rather far from 

 the apical pole being essential differences from the latter species; also the prominent red colour of 

 the pharyngeal folds is a difference from PI. piletis, in which these folds are generally much less con- 

 spicuously coloured, faint violet or yellowish. Anything definite cannot, however, be said about this 

 question, because Torrey gives no information at all [about the specimen figured. If it is a grown 

 specimen, it ma)- represent a new species; if it is a yong specimen magnified, it may not be impossible 

 that it will prove to be identical with PI. piletis. 



Damas & Koefoed in "Le Plankton de la Mer du Gr6nland"3) (p. 414) state that Pl.pileus 

 "manque tout a fait en plein ocean". I do not think this statement quite justified. In the collection 

 of the Copenhagen Museum there are some specimens taken at 50° 20' N. 30° 10' W. (4. VI. 1889, by 

 Lieutenant Ulrich, on the Corvette "Dagmar"), which I think are undoubtedly Pl.pileus. By the 

 German South Polar Expedition a specimen was taken between Ascension and the Cap Verde Islands 

 (Moser, Op. cit. p. 143). These facts show that the species can, in any case occasionally, be found in 

 the open sea and is not wholly bound to the coastal waters. 



From the Greenland seas Pl.pileus is generally recorded in literature, e.g. by Liitkeni), 



■) K, M. Levander. Forekomsten af Cteuophorer i Ostersjon. Medd. af Soc. pro Fauna et Flora Feniiica. H. 25. 

 1900. p. 104. 



') Moser (Op. cit. p. 145) regards Pleurobiachia hachei h.%as&. as synonymous with PL piktts, suggesting the characters by 

 which it is stated by Agassiz to differ from pileiis ( rhododactyla) to be due to "Unterschiede in der Kontraktion . . . oder aber auf 

 einem zufalUgen Unterschied beruhf. It does not appear very probable thafflTe main character, the position of the opening 

 of the tentacle sheath adorally to the opening of the adradial into the meridional vessels, could be due to contraction. But this 

 form very much needs to be more carefully studied than has hitherto been the case. 



3) Due d' Orleans. Croisiere oceanographique dans la mer du Gronland en 1905. 



4) C. F. Liitken. A revised list of the Acalepha; and Hydrozoa of Greenland. Arctic Manual. 1875. p. 187. (Pleuro- 

 brachia rhododactyla Agass.). 



The Iiigolf Expedition. V, 2. lO 



