MEDUSA. I. 



as occurring at the coast of Greenland 1 , it is due to L tit ken who, not being aware of the mistake 

 of Agassi z, included the species in his list of the medusae of Greenland, whence it proceeded 

 to the lists of Winther and Fewkes. This is rather annoying, it is true, and may, possibly, still in- 

 volve misunderstandings; but I am not able to comprehend, how this danger might in any way be 

 removed by the introduction of the name Melicertidium in the place of MelicertTtm. 



Altogether, it seems to me that the use of the generic name Melicertum involves no 

 danger any more for a continuation of the confusion. Since 1843 the names Melicerta and Melicertitm 

 sensu Peron & Lesueur, Oken, Eschscholtz have been applied to no other species than campanula. 

 "Medusa campanula" Fabricius has to be excluded from the system, as it has nbt been identified with 

 certainty, and all records of ''Mel^cert^^m campanula' 1 '' from Greenland have to be omitted. When this 

 is remembered, nobody can have any doubt as to the meaning of the names Melicertum campanula 

 Agassiz, Meh'certum georgicum Agassiz, and Melicertum octocostalum (Sars). 



When, thus, Meh'certum Agassiz cannot involve misunderstanding this generic name seems to 

 me to be preferable to Melicertidium, because Melicertum is older and is correctly defined, whereas 

 the definition of Melicertidium is incorrect. 



The species of the genus Melicertum. 



Melicertum proboscifer Maas (1897, p. 19) is undoubtedly a Trachymedusa. Mayer (1910, 

 p. 209) includes Melicertella panocto Haeckel among the species of Melicertum, though he indicates 

 the possibility that it may belong to the genus Melicertissa. In any case, the presence of ocelli on 

 the base of the tentacles excludes the species from the genus Melicertum. 



Melicertum georgicum A. Agassiz (L. Agassiz 1862, p. 349; A. Agassiz 1865, p. 135) seems to 

 differ but very slightly from Melicertiim campanula Agassiz; but since the species was described, no 

 medusa belonging to the genus Melicertiim has been found in the Pacific; it is impossible, therefore, 

 to state, whether it is identical with the Atlantic-American species. Melicertum georgicum is found in 

 the Gulf of Georgia on the west coast of U. S. A. 



The two Atlantic species, the European Melicertum octocostatum Sars and the American M. 

 campanula Agassiz, are undoubtedly nearly related. In the first-mentioned species the height of the 

 bell is about 12 mm, the diameter about as much or a little smaller, and there are fairly constantly 

 64 longer and 64 shorter tentacles. In Melicertum campanula the height and the diameter amount to 

 about 25 mm, and in the full-grown individual the tentacles are all alike; Agassiz and (after him) 

 Mayer state their number to be about 70. There does not seem to be any important difference with 

 regard to the shape of the bell, the manubrium, or the gonads. In campanula, it is true, the gonads 

 are said to reach entirely to the circular vessel, whereas in octocostatum a small distal part of each of 

 the radial canals is free of gonads; but this feature may, as in other medusae, be subject to much 

 variation. The tentacles of octocostatiim are going to be further mentioned below; here I shall only 

 remark that there is no decisive difference between the two series of tentacles. Melicertum catnpanula 

 might very well be considered as a variety which attains a more exuberant development, i. e. when 

 the individual is mature it has a comparatively large size, and all of the tentacles are developed to 



1 My record of Melicertum campanula as occurring at Frederikshaab in Greenland (1913, p. 268 and 19141 P- 424) is 

 due to a mistake which I very much regret. 



7' 



