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Show 1903.] MEDUS.E FROM BRITISH COLUMBIA AND ALASKA. 187 Holl, Mass. Here it was represented by what was thought to be a second species. Two years later Dr. Mayer confirmed this opinion, adding that Prof. Agassiz pronounced the Woods Holl form different from the Pacific form G. vertens, and Mayer (29) proposed the name G. murbachii. Agassiz and Mayer (3) described a new species, G. suavensis, from Suava Harbour, Fiji Islands. Again, Mayer (28) concluded that his Cubaia aphrodite was really a species of Gonionemus. The development of Gonionemus seems to indicate that it belongs to the lower Trachomedusa?; there are also other features that put it in the lower Trachomedusa?, such as the position of the otocysts, gonads, the marginal welt of nettling-organs, and the insertion of the tentacles. Until the life-history of one of the species is better known it is difficult for the present to determine its further position. Provisionally, Haeckel's family Petasida?, subfamily Petachnince, with four radial canals, otocysts either free on the margin or enclosed, tentacles hollow, is best fitted for its reception. It might then be placed between the genera Aglauropsis and Gossea. With the exception of the number and position of the tentacles, the above characters are so constant in the four species now known that we can look forward to their being found in all true members of the genus. The position and insertion of the tentacles will vary most. Only a few Medusa? are recorded, Bathycodon, Pectantis, <kc, in which the ends of some or all of the tentacles are provided with means for clinging to foreign objects. But these are not of the same nature nor in the same position as are the suctorial pads of Gonionemus. Recently, Mayer (27) has found a new Medusa, in which every fourth tentacle has an adhesive pad that corresponds somewhat with the position of that in Gonionemus, though unlike it in appearance. This Trachomedusa, he thinks, is closely related to Gonionemus, and has indicated this in calling it Gonionemoides. There is no reason why the presence of these pads, if morphologically the same, may not be one of the marks of relationship. The fact that the young of Gonionemoides geophila have pads on every alternate tentacle, not on every fourth as in the adult, may indicate that in the ancestral form they were so arranged. In this case Medusa? having adhesive pads on every alternate tentacle would be more closely related to Gonionemoides than to Gonionemus, or possibly would be intermediate forms such as Gonionemus {Cubaia) aphrodite Mayer, in which every other tentacle possesses an adhesive pad. Behaviour, where it is well marked or there are special habits as in this case should enter into the characters of the genus or at least the species description. The peculiar habit of swimming to the surface of the water and turning over to float lazily downward is well marked in both G. vertens and G. murbachii, and we may |
