32 THE VOYAGE OF H.M.S. CHALLENGER. 



nematophore wliich lies below the hydrotheca is fixed, and resembles that of the ordinary 

 Statoplean genera in all respects, except in the fact of its being quite detached from the 

 hydrotheca, and in the presence of an imperfect septum close to its distal extremity, thus 

 showing a tendency to the bithalamic form of the Eleutheroplean nematophore. 



In all other important points the species on which the genus Heteroplon has been 

 founded presents the essential features of the Eleutheroplea, with which, notwithstanding 

 the presence of a fixed nematophore, it must be associated. 



Heteroplon pluma, n. sp. (PL VIII. figs. 1-3). 



Tropliosome. — Colony attaining a height of about four inches; stems sparingly branched 

 monosiphonic, springing in groups from a creeping stolon ; hydrocladia about one-fourth 

 of an inch in length, carrying a hydrotheca on every internode, a hydrotheca also carried 

 by the stem close to the origin of every hydrocladium, stem with groups of two or 

 three short internodes at irregular intervals. Hydrothecse with entire margin, adnate to 

 the rachis by about three-fourths of their height ; lateral nematophores borne each on a 

 short process of the hydrothecal internode ; hydrotheca! internode also carrying a single 

 moveable nematophore at the distal side of the hydrotheca ; mesial fixed nematophore 

 close to the proximal end of the internode, in the form of a short, blunt, somewhat curved 

 spine, with an oblique terminal orifice. 



The hydrothecal pinnse of the present species are closely set along the stem, and the 

 general habit of the colony is more that of an Aglaophenia than of a Plumularia — a feature 

 which is not without interest when viewed in connection with the presence of the fixed 

 nematophore. Notwithstanding, however, the presence of a fixed nematophore, and the 

 Aglaophenia-like habit of the species, the whole assemblage of characters is so decidedly 

 that of the Eleutheroplean Plumularidse, that there need be no hesitation in assigning it 

 to this group. 



The specimen was dredged at Station 162, AprU 2, 1874, ofi" East Moncoeur Island, 

 Bass Strait, from a depth of 38 to 40 fiithoms ; bottom, sandy. 



Sub-family — S tatoplea. 

 Section — Phylactocaepa. 



Acanthocladium, nov. gen. 



Name from uKavOa, a thorn, and kXciSos, branch, in allusion to the spiny terminations of the 

 branches. 



GE?fERic Chaeactee. Tropliosome. — Distal portion of branches destitute of hydro- 

 cladia, whose places are taken by a long, spine-like appendage on each internode. 



Gonosome. — Phylactocarp replacing a hydrocladium, and consisting of a rachis with 



