MEDUSAE. I. 89 



waters of Iceland and Greenland the season of its appearance falls somewhat later, in accordance with 

 the later commencement of the spring. Young specimens may be found at the northern coasts of Ice- 

 land as late as in June, and at Iceland as well as at the west coast of Greenland full-grown specimens 

 may still be met with in August 



Family Eucopidae Gegenbaur. 

 Genus Obeli a Peron et Lesueur. 



Three species of the hydroid genus Laomedea producing free-swimming medusae (Obelia] occur 

 in the North Atlantic area, viz. Laomedea geniculata, dichotoma, and longissima, all of which are very 

 widely distributed. Several authors have tried to find characters serviceable for separation of the 

 medusae of these species, but up to now the results have been very poor. The question has especially 

 been dealt with by Browne. In 1900 he described a new species, Obelia nigra, easily recognizable on 

 account of some of the tentacular bulbs (about 6 in each quadrant in full-grown medusae) being double 

 the size of the others and provided with dark pigment. Browne is now of the opinion that Obelia 

 nigra is the medusa of Laomedea longissima. Browne has succeeded in rearing the medusae of the 

 two other species and keeping them alive in aquaria for a considerable time, but he has told me that 

 there is no traceable difference between the medusae of the two species. I myself has likewise tried to 

 rear the medusae of the three species of Obelia during a stay in Plymouth in 1914. I think that I have 

 found certain characteristical differences between the species in the early stages, but I was not able 

 to make the specimens grow very much in the aquaria, evidently because I did not give them the 

 right kind of food. Later on, in 1916, I have tried to keep Obelia geniculata in plunger-aquaria in the 

 laboratory for zoo-physiology in Copenhagen, but here the question of food-supply was still more diffi- 

 cult. Some of the specimens lived in the aquaria for several weeks, but they did not increase in size. 

 I have, however, not yet relinquished all hope but that I shall succeed sometimes in solving the 

 problem of the difference between the three species, but for the present we must leave the matter in 

 abeyance. 



In the following I shall give a list of the North-Atlantic material of Obelia at my disposal, 

 first recording the specimens which may be referred with certainty to Obelia nigra, and then the others 

 which may not at present be specifically identified. 



Obelia nigra Browne. 



Obelia nigra Browne 1900. Fauna and Flora of Valencia Harbour. --Proceed. Roy. Irish Acad. Ser. 3. 

 Vol. V. p. 721. 



Material: 

 Iceland: 



1) Lat. 66i7' N., Long. I427' W., near Cape Langenaes. July 2Oth 1904. Depth 77 m. Young- 

 fish trawl, 80 in wire. "Thor" stat 203(04). -- 2 specimens. 



2) Ingolfsfjord. July I2th 1902. "Diana", A. Ditlevsen. -- 8 specimens, partly very large. 



3) Hesteyrifjord. June 25th 1902. Surface. "Diana", Ditlevsen. - 9 specimens. 



The Ingolf- Expedition. V. 8. 12 



