No. 5-] VARIATION AMONG HYDROMEDUSAE. 243 



While no emphasis is placed on this feature of variation, it is 

 yet worthy of note in comparison with such medusae as 

 Coryne, Dipurena, etc., in which the greatly elongated manu- 

 brium feature is rather distinctive. 



In Fig. 14 is shown an interesting and anomalous feature 

 which is more or less monstrous, namely, a spike-like growth 

 from one side of the basal portion of the 

 manubrium. While in some respects it 

 might be comparable with an oral tentacle 

 of Margelis or Nemopsis, still only in a 

 somewhat remote way. It was rather 

 rigid, yet devoid of any chitinous or other Fu - M. --Semidi. ls ,ammatk 



sketch of manubrium of 



rigid support. As will be seen, it has the medusa showing anomalous 



r r i projecting spur, S. 



form or an elongate, attenuate process, 



about twice the length of the manubrium. It would seem, as 

 suggested above, to be a wholly unique if not anomalous struc- 

 ture, without evident correlation with, or adaptation to, any 

 other organ or function. 



Tentacles. 



As compared with Eucope, Obelia, Podocoryne, and many 

 other genera, there seems to be a very different order and 

 relationship among the tentacles of Gonionemus. In the small- 

 est specimen measured the diameter was but 2 mm., and the 

 number of tentacles twenty-nine. The largest specimen found 

 measured 19 mm., and the number of tentacles was sixty-eight. 

 That mere size is not, however, determinant of numbers will 

 be seen when it is stated that a specimen measuring 4 mm. 

 had thirty-nine tentacles, while one measuring 6 mm. had 

 but thirty. While, as stated above, the largest measured speci- 

 men had sixty-eight tentacles, two others measuring 15 and 16 

 mm., respectively, had each seventy-two tentacles, and a speci- 

 men measuring 14 mm. had seventy-one tentacles. While it 

 should be stated that these observations were made upon speci- 

 mens preserved in formaldehyde, which may have thereby suf- 

 fered some shrinkage, still since the preservative was in all 

 cases the same medium and of the same, or very nearly the 

 same, per cent, they would presumably be similarly affected. 



