﻿April, 1857.] 



ELLIOTT SOCIETY. 



213 



For instance, Stauridium is a link of close connection between 

 Tubularidae and Corynidae, and researches into the embryology of 

 Velellidse and Siphonophorse, coupled with the discovery of new 

 forms may lay open to our view closer connections with the two 

 former groups than are yet apparent. In fact the free floating 

 larva of Nemopsis, with its medusa-buds, may already furnish a 

 suggestion as to what may possibly be the unknown embryonic 

 condition of the Siphonophorae. And this is not rendered less 

 probable by the fact that Lizzia which belongs to the same group, 

 (Hippocrenidse) as Nemopsis, exhibits an instance of the same 

 tendency to gemmation in the medusa-stage, which is character- 

 istic of all the genera included at present among Siphonophorse. 

 Whether the dividing line now drawn between the larval forms of 

 Campanularidae and Sertularidse, will always remain as distinct 

 as it seems at present, must be determined by future researches, 

 but my own observations lead me to suspect that it will not. 

 With regard to such minor groups as Circeadae, Trachynemidce, 

 Stomobrachidae, Geryonidae and iEquoridae, the embryology of only 

 one of them, Trachynernidae, is even yet guessed at, and that ex- 

 hibits some analogy with the embryology of the iEginidae, a very 

 different group. The very fact that researches hitherto among 

 fixed Hydroids have not yet discovered the larvae of these groups, 

 renders it probable that, like those of Trachynernidse and 

 iEginidae, they are free swimming Hydroids. Yet the forms of 

 these minor groups, (though the discovery of new genera may 

 possibly diminish their number, by uniting two or more of them,) 

 are in the main quite distinct and probably sufficiently so to dis- 

 tinguish' them as families, even should their embryology be found 

 to exhibit a character common to them and the iEginidae. 



I therefore reiterate the remarks made at the opening of these 

 descriptions, that the families of Hydroid Medusae will probably be 

 found more numerous than those which have hitherto been founded 

 among the fixed hydroids, the Siphonophorae, and the free, oceanic 

 Exostomata. In other words, that the greater groups which, in this 

 monograph I have endeavored to distinguish as faithfully as pos- 

 sible, in accordance with such information as I have, will be found 

 untenable in a natural classification, and that the minor groups^ 

 considerably modified, perhaps, from the form in which I have at 

 present given them, will be, nevertheless, found to be the true 

 family groups of Hydroidea. 



