56 
THE VOYAGE OF H.M.S. CHALLENGER. 
Gonosome. — Gonangia each springing from a point just below a hydrotheea, elongated 
ovate, tapering below into an ill-defined peduncle, strongly annulated, with a terminal 
obscurely four-toothed orifice. 
Locality . — Station 315, Port William, Falkland Islands; lat. 51° 40' S., long. 57° 
50' W. ; depth, 5 to 12 fathoms. 
There do not appear to be any legitimate grounds for separating the form here 
described from the widely distributed Sertularia polyzonias. Though the specimen 
is scarcely more than an inch in height it has probably attained nearly its full size, 
as the presence of a well- developed gonosome would seem to indicate. It is thus of 
much humbler habit than the typical Sertularia polyzonias, from which it further differs 
in the more elongated and more deeply annulated gonangia. These differences, however? 
I regard as merely local variations to which we should not be justified in assigning a 
specific value. The membranous valves of the hydrotheca had not been preserved so as 
to be recognisable in the specimen. 
The specimen here described was dredged in the region of the Falkland Islands. The 
collection also contains specimens obtained at Port William, which I do not hesitate to 
refer to the same species. 
Sertularia exserta, n. sp. (PI. XXVII. figs. 1, la, lb, lc). 
Trophosome. — Hydrocaulus monosiphonic, slender, subdichotomously and profusely 
branched, divided by distinct joints into internodes, each of which carries a hydrotheca. 
Hydrothecse exactly alternate, each borne at the distal end of an internode, adnate 
to the internode for about one-third of their height, deep, nearly cylindrical, margin 
of orifice with two strong cusps at its apocauline side, and one at its epicauline side. 
Hydranths incapable of complete retraction within the hydrothecse. 
Gonosome. — Gonangia springing each from a point just below the base of a hydro- 
theca, oviform, encircled by very prominent transverse annular ridges, and terminating 
distally in a short neck with a saucer-like terminal expansion which carries the orifice. 
Locality. — Station 151, off Heard Island; depth, 75 fathoms. 
Sertularia exserta is a very beautiful and interesting species. Its hydranths, like 
those of Thuiaria hyalina (PI. XXXIII. figs. 2, 2a), are incapable of complete retrac- 
tion, the tentacular crown being never withdrawn into the hydrotheca ; and here also 
as in that Hydroid the body of the hydranth sends off in all directions fleshy bands 
(fig. la) by which it becomes tied to the hydrotheca-walls, and is thus rendered incapable 
of that complete retraction by which in ordinary cases the hydranth is enabled to retire 
within the cavity of the hydrotheca. 
In this imperfect retraction of the hydranth we have a condition which may be 
