54 THE VOYAGE OF H.M.S. CHALLENGER. 
Gonosome.—Gonangia springing from the stem, and destitute of special protective 
apparatus. 
The genus Azyyoplon is essentially characterised by the very exceptional condition 
of having no lateral nematophores—a condition which, except in Diplocheilus, does not 
occur elsewhere among the known genera of Plumularide. So far as is yet known, 
Azygoplon is represented by one species only. 
Azygoplon vostratum, n. sp. (Pl. XEX. figs. 1-3). 
Trophosome.—Colony attaining a height of upwards of three inches ; stem much and 
irregularly branched, monosiphonic ; hydrocladia about two-tenths of an inch in length. 
Hydrothecee rather shallow, with one strong marginal tooth on each side, and a long 
beak-like process in front; mesial nematophore adnate for its entire length to the 
anterior wall of the hydrotheca, and then bearing on its summit a free membranous 
scoop-shaped appendage. 
Gonosome.—Gonangium nearly spherical, narrowed into a short stalk at its point of 
attachment to the stem close to the base of a hydrocladium. 
This is a very remarkable Hydroid. The form of the hydrotheca is exceptionally 
striking, for instead of the serrated margin usual in the Statoplean Plumularidee, this 
condition is here replaced by a single strong tooth on each side and a long beak-like 
projection of the margin in front. The mesial nematophore 
the only one present in the 
genus—is divided into two portions by a transverse joint ; the proximal portion is the 
proper nematophore, and is, as in the mesial nematophore of other Statoplean forms, a 
simple continuous projection of the hydrothecal internode, and is adnate for its entire 
length to the anterior walls of the hydrotheca; the distal portion consists of a free 
membrane bent into a scoop-shaped form, the concavity of which is turned towards the 
hydrotheca and embraces its anterior wall. 
The stem is divided into internodes by transverse joints, and every internode gives off 
from alternate sides a hydrocladium. The joints by which the internodes of the hydro- 
cladia are separated from one another are unusually well marked—a feature in which 
Azygoplon rostratum approaches the Eleutheroplean rather than the Statoplean forms. 
The specimen had been broken away from its hydrorhizal end, and on this account 
no exact assertion can be made of the height which the species may attain. 
Azygoplon rostratum comes very near to a species described and figured by Kirchen- 
pauer under the name of Aglaophenia avicularis, from specimens brought from Bass 
Strait. If it were not for the very different form of the mesial nematophore, I should 
have regarded the Challenger species as identical with that of Kirchenpauer. 
Dredged at Station 161, April 1, 1874, off the entrance to Port Philp; depth, 38 
fathoms ; bottom, sandy. f 
