with Observations on Australian Hydroids. 79 



fectly movable, and would come under the genus as limited 

 by Professor Allman. P. ohliqua and the three following 

 species agree in having only a single hydrotheca on each 

 pinna. In P. delicatula the anterior sarcothecse are small, 

 and, though agreeing in all essentials with those of the 

 abovenamed species, seem more rigid, always retaining the 

 same position, at least when dry. In P. campanula the 

 supracalycine, as well as the anterior sarcothecse, are short 

 and stout, and so firmly attached as to prevent any varia- 

 tion of their position. If forcibly pushed aside they instantly 

 assume their normal position on removing the pressure. 

 Notwithstanding the fixed nematophores, this species is 

 described by Professor Allman in the Report as a Plumularia, 

 under the name of P. laxa. The other species described in 

 the " Catalogue" which have the anterior sarcotheca im- 

 movable, and curved towards the hydrotheca, are P. BusJdi, 

 P. aglaoplienoides, P. Goldsteini, P.filicaulis, P. coiapressa, 

 P. Australis, and probably P. ohconica. P. compressa and 

 P. Australis agree with P. ohliqua and its immediate allies 

 in having only one hydrotheca on each pinna, but differ in 

 the stout fixed anterior sarcothecse, which look like project- 

 ing portions of the hydrocaulus. In several of the species 

 the sarcotheca is so strongly curved towards the calycle as 

 to seem almost appressed to it. 



It will be seen, therefore, that among the Australian Eleu- 

 theroplea the fixed condition of the anterior sarcothecse is 

 by no means rare, as, according to Professor Allman, it is in 

 the sub-family generally, and that, in fact, it obtains in at 

 least half our species. As it is not constantly associated 

 with any peculiar form of the sarcotheca, but depends merely 

 on its relative size at the point of attachment and the firm- 

 ness of the perisarc, and does not imply any important 

 structural distinction, it seems best to include all the species 

 under the genus Plumularia — in other words, to continue to 

 take that genus in the sense in which it is used by Hincks, 

 Kirchenpauer, and most other recent writers on the Plumu- 

 lariidse. I would further suggest that the other Eleuthero- 

 plean genera should be made sufiiciently comprehensive to 

 include species which difier from each other only in the 

 fixed or movable condition of the anterior sarcothecse. 



Halopteeis, Allman. 



Hydrocladia pinnately arranged; mesial sarcothecse not 

 adnate to the hydrotheca ; laterals fixed, adnate. 



