78 
THE VOYAGE OF H.M.S. CHALLENGER. 
Gonosome . — Gonangia borne on peduncles which spring from within the cavity of 
certain hydrothecse, where they take the place of the hydranths. 
The genus Synthecium was originally characterised by me from a New Zealand 
Hydroid in the collection of Mr. Busk. It forms one of the most definitely marked 
generic groups among the Calyptoblastic Hy droids, and in the singular relation of the 
gonosome to the hydrothecse is absolutely unique. This relation is found in the fact 
that the peduncles of the gonangia are enclosed each within the cavity of a hydrotheca. 
The cavity is completely filled by the peduncle, which thus takes the place occupied in 
other hydrothecse by the hydranth, and has its coenosarc directly continuous through 
the base of the hydrotheca with the coenosarc of the stem ; the hydrothecse which thus 
carry gonangia differ in no respect, either in form or in position, from those which 
continue to exercise their normal function of giving protection to the hydranth. 
To this condition we have a very interesting parallelism in the genus Tliecocladium 
(p. 80), in which, as in Synthecium, the usual function of certain hydrothecse becomes 
changed into another. Here, however, the place of the hydranth is taken, not by any 
part of the gonosome, but by the origin of a branch which in Thecocladium occupies the 
cavity of the hydrotheca exactly as the peduncle of the gonangium does in Synthecium. 
In Thecocladium the gonangia spring as usual from the side of an internode. 
Since the first determined example of the genus was described under the name of 
Synthecium elegans, 1 another closely allied to this and possibly only a variety of it has 
been characterised as Synthecium ramosum . 2 To these the Challenger collection now 
contributes two very distinct and well-marked species, one of which differs from all the 
others described in the fact of its having its hydrothecse alternate instead of opposite. 
Synthecium campylocarpum, n. sp. (PL XXXVII. figs. 1, la, lb, lc). 
Trophosome . — Stem simple, monosiphonic, set with pinnately disposed opposite 
ramuli ; pinnse divided into equal internodes by well-marked joints, every internode 
carrying a pair of hydrothecse. Hydrothecse strictly opposite, tubular, cylindrical, with 
circular even orifice. 
Gonosome . — Gonangia (female?) pod-shaped, compressed, slightly curved towards 
the supporting pinna, the two wider sides carrying closely set, prominent, transverse 
ridges, which thin away towards the edges of the gonangium where they finally disappear. 
Male (?) gonangia oviform, destitute of the transverse ridges, and with the axis straight. 
Locality . — Off Port Jackson ; depth, 30 to 35 fathoms. 
Synthecium campylocarpum presents in its trophosome little to distinguish it from 
Synthecium elegans, the first described species of this remarkable genus. The elongated, 
1 Journ. Linn. Soc. Lond. (Zool.), vol. xii. p. 266, pi. xv. 2 Ibid., vol. xix. p. 137, pi. xii. 
