82 
THE VOYAGE OF H.M.S. CHALLENGER. 
from which they are emitted to give any indication that these are destined for branches 
and not for hydranths. 
The gonangia are borne along the stems and branches. They spring each from a 
point just below a hydrotheca, and extend over a space corresponding in height to that 
of about three consecutive hydrothecse. They are oboviform and strongly annulated, 
but are closely pressed to the hydrocaulus, and in consequence present at their epicauline 
side a deep, longitudinal furrow, whose sides overlap the hydrocaulus, and into which the 
annulation does not extend. Their summit carries the sessile, elliptical orifice. 
The specimens have a height of between two and three inches, and were dredged in 
Simon’s Bay, from a depth of 10 to 20 fathoms. 
In a collection of Hydroids belonging to Miss H. Gatty is a small dry specimen of 
a Hydroid from an unknown locality, which, notwithstanding some slight differences, must 
be referred to the species here described. 1 It differs from the Challenger specimen in 
having the orifice of the hydrotheca surrounded by a slightly thickened rim. The 
hydrotheca was probably prolonged beyond this rim by a membranous extension of its 
margin, but in the dried t specimen nothing but a faint indication of this could be detected. 
Another feature, probably transitory, in Miss Gatty’s specimen, consists in the 
presence of a delicate diaphragm, apparently chitinous, which intersects the hydrotheca 
obliquely, passing from a point near the middle of the apocauline wall downwards to a 
point on the epicauline wall a little above the base of the hydrotheca. No trace of these 
diaphragms was present in the specimens collected by the Challenger. The diaphragm 
is apparently complete and strongly recalls the so-called epiphragm excreted by certain 
snails as a defence against the injurious action of climate and other unfavourable 
surroundings. 
I am not disposed to regard either of these differences as affording grounds for 
specific separation. It is by no means improbable that the diaphragm seen in the 
hydrotheca is a temporary structure excreted over the retracted hydranth for protection 
during a resting or inactive period of its existence ; and the differences between the two 
forms ought probably to be regarded as pointing to different states of one and the same 
species. 
No gonosome was present in the specimen contained in Miss Gatty’s collection. 
Family IDIIDiE. 
Character of the Family. Trophosome . — Hydrothecse adnate to the hydrocaulus. 
Coenosarc divided into segments which form two longitudinal series of intercommunicating 
chambers, each of which corresponds to a hydranth, with the gastral cavity of which it 
is continuous. 
1 See Journ. Linn. Soc. Lond. (Zool.), vol. ix., March 1885. 
