26 
THE VOYAGE OF H.M.S. CHALLENGER. 
cavity so reduced by the great thickness of its chitinous walls as to be incapable of 
receiving the hydranth in retraction. 
Gonosome. — Gonophores in the form of simple sporosacs developed within chitinous 
gonangia, which spring, aggregated or scattered, from the creeping stolon. 
The genus Hypanthea was founded for a Calyptoblastic Hydroid brought home from 
Kerguelen Island by the section of the Transit of Venus Expedition whose observations 
were carried on in that island. 
The species obtained by the Transit Expedition is distinct from that dredged by the 
Challenger off the same island, and differs still more widely from another species of the 
same genus obtained by the Challenger off the Falkland Islands. 
The genus is very remarkable, the place of the hydrothecse being taken by bodies 
which differ from proper hydrothecse in having the cavity so reduced by the great 
thickness of the chitinous walls, that they may be said to support rather than contain the 
hydranths, which are thus nearly as much unprotected as the hydranths in Halecium, 
where the hydrothecse remain in a condition quite rudimental. 
Hypanthea aggregata , n.- sp. (PI. XIV. figs. 1, la). 
Trophosome . — Hyrocaulus a creeping and reticulated stolon, from which are emitted 
scattered simple peduncles ; peduncles about a quarter of an inch in height, cylindrical, 
smooth, with a swollen summit which, through the intervention of a single globular 
segment, supports the hydrotheca. Hydrothecse obconical, compressed, with oblique 
entire margin. 
Gonosome. — Gonangia (female) springing like the peduncles of the hydrothecse from 
the creeping stolon, densely crowded, fusiform, each tapering below to its point of 
attachment without forming a definite peduncle, and terminating distally in a laterally 
compressed orifice. 
Locality . — Kerguelen Island ; depth, 20 to 26 fathoms. 
The present species differs from Hypanthea repens of the Transit of Venus 
Expedition in its densely aggregated instead of scattered gonangia. These form in 
Hypanthea aggregata a densely crowded mass, and the hydrostyles, instead of arising 
in the intervals of the gonangia, spring separately from the stolon. The gonangia in 
the Challenger specimen are exclusively such as contain female sporosacs, thus again 
differing from those of Hypanthea repens, in which it would appear that the colony 
may be monoecious, male and female gonangia being there associated on the same 
stolon. 
The cavity of the hydrotheca is represented by a comparatively shallow saucer-like 
depression, prolonged by a narrow canal which extends downwards nearly in the axis of 
