32 THE VOYAGE OF H.M.S. CHALLENGER. 
nematophore which 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. 
Leteroplon pluma, n. sp. (Pl. VIII. figs. 1-3). 
Trophosome.—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. Hydrothecee 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 ; hydrothecal 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 pinnee 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 Plumularidee, that there need be no hesitation in assigning it 
to this group. 
The specimen was dredged at Station 162, April 2, 1874, off East Moneceur Island, 
Bass Strait, from a depth of 38 to 40 fathoms ; bottom, sandy. 
Sub-family—S TATOPLEA. 
Section—PHYLACTOCARPA. 
Acanthocladium, nov. gen. 
Name from dkavOa, a thorn, and «Addos, branch, in allusion to the spiny terminations of the 
branches. 
Generic CHaracter. Trophosome.—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 
