REPORT ON THE HYDROIDA. 33 
two series of pinnately-disposed, alternate, free ribs, each rib carrying near its base a 
hydrotheca. Gonangia springing from the rachis. 
The remarkable mode in which the branches of Acanthocladium terminate, recalls the 
very similar condition presented by the genus Acanthella ; but while Acanthocladium is 
a Statoplean form, Acanthella belongs to the Eleutheroplea. The gonosome of Acanthella 
is unknown, but the specimens of Acanthocladium hualeyi the only species of the 
genus as yet discovered, are, on the contrary, abundantly provided with this important 
element of the colony. The phylactocarp of Acanthocladium belongs to the same type 
as that of the Aglaophenia distans and Aglaophenia bispinosa of the Gulf Stream Report," 
every rib carrying, as in these last, near its base a modified hydrotheca, The distal portion 
of the rib is in all these cases the greatly modified mesial nematophore of this hydrotheca, 
while the proximal portion is a peduncle which springs from the rachis and supports the 
modified hydrotheca and its appendages. (See p. 11). 
Acanthocladium hualeyi, Busk, sp. (Pls. [X. and XX. figs. 1-8). 
Plumularia hucleyi, Busk, Voyage of the ‘ Rattlesnake,” vol. i. p. 395, 1852. 
Trophosome.—Colony attaining a height of fifteen inches; stem fascicled, springing from 
a dense cushion of fine entangled tubes, undulated, giving off pimnately-disposed alternate 
simple branches about two inches in length, which carry the hydrocladia and terminate each 
in a jointed prolongation which is composed of numerous (twelve to sixteen) internodes, 
every internode carrying a slightly curved spine, which is supported on the extremity of 
a short process from alternate sides of the internode, and carries two rows of small cup- 
shaped nematophores ; hydrocladia alternate, short, about one-tenth of an inch in length. 
Hydrothecxe approximated, wide and rather shallow, with an anterior parietal fold and a 
very short intrathecal ridge; orifice of hydrotheca with its plane parallel to the axis of 
the short internode, margin crenate ; mesial nematophore adnate to the entire height of 
the hydrotheca wall, and then continued as a long, free, curved spine which arches over the 
orifice of the hydrotheca ; lateral nematophores short, crescentic. 
(ronosome. 
branches near their middle, every series having the unmodified hydrocladia at its proximal 
Phylactocarps developed in a continuous series on each side of the 
and usually also at its distal side; costa of phylactocarp twenty-six to thirty in number 
springing alternately from the sides of the rachis, over which they arch, each carrying a 
double row of cup-shaped nematophores, and at about one-third of its length from the 
base, a single small deep hydrotheca. Gonangia ovoid, springing from the rachis, each 
close to the origin of a costa. 
The long flexile undulating stem and simple plume-like branches of Acanthocladium 
1 Allman, Report on the Hydroida collected during the exploration of the Gulf Stream, by L. F. De Pourtalés, United 
States Coast Survey, 1877, p. 44, pl. xxvi. figs. 1-8, and p. 46, pls. xxvii., xxvill. 
(ZOOL, CHALL, EXP,—PART xx.— 1883.) U5 
