HYDROIDA. BALE. 265 



Genus SYNTHECIUM, Allman. 

 SYNTHECIUM SUBVENTRICOSUM, Bale. 



Synthecium subventricosum, Bale, Biological Results 

 "Endeavour/' ii., 1, 1914, p. 5, pi. i., figs. 3-5. 



Loc. Great Australian Bight, 40-100 fathoms, on large 

 Plumularians. 



Genus HYPOPYXIS, Allman. 

 HYPOPYXIS DISTANS, Bale. 



Hypopyxis distans, Bale, Biological Results " Endeavour,'" 

 ii., 4, 1914, p. 167, pi. xxxv., figs. 2-5. 



Unless further research should prove the pouch-like 

 structures peculiar to this hydroid to be of greater importance 

 than at present appears, it seems to me that the retention of 

 the genus will not be justified. In that case the species will 

 fall naturally into the genus Thuiaria, as understood by 

 Levinsen. I have referred to the close correspondence 

 between H. distans and Sertularia tuba (which latter Levinsen 

 mentions among the Thuiarice), and I may add that the 

 chitinous prolongations below the hydrotheca3 (" stalk- 

 marks ") are quite similar in the two forms, though in my 

 figure of S. tuba, (being the superficial view only), they do not 

 appear. 



I have examined many hydrotheca? of H. distans, in the 

 hope of finding some clue to the significance of the hydro- 

 thecal pouches, but have not succeeded. As to their origin, 

 it is clear from their appearance in optical sections that their 

 inner wall is composed of two layers of perisarc which are 

 united. It is as if an invagination of the perisarc had oc- 

 curred just above the base of the hydrotheca, directed 

 upward, and that the two adjacent walls of the invagination 

 had united, forming an erect perisarcal ridge, which is the 

 inner wall of the pouch ; or (which would have the same 

 optical effect), as if a pouch-shaped protrusion of the hydro- 

 thecal wall had been directed downward, overlapping that 

 part of the hydrotheca below it, and becoming closely united 

 therewith. Whichever has happened, the whole has been 

 ensheathed in a thin outer layer of perisarc, and the pouch 

 remains as an extremely contracted chamber completely 

 continuous with the general cavity of the hvdrotheca. 



Locs. Great Australian Bight, Long. 126' 45^' E., 190-320 

 fathoms ; Long. 130 40' E., 160 fathoms ; Long. 127 20' E. ; . 

 180 fathoms. 



