SYDNEY J. HICKSON anp F. H. GRAVELY. 
lor) 
It is possible that this species of Perigonimus is identical with the one obtained 
by the ‘Belgica’ in 71° 15' S. and 87° 39’ W. (8: pp. 8-9; Pl. L, fig. 2); but 
Dr. Hartlaub had not the good fortune to be able to examine and report upon the 
gonophores. 
The hydrosome has also some resemblance to that of the British species 
P. coccineus (Wright, see Hincks, 11: pp. 97-98) of which the gonophores are not 
known. 
Of the better known British species it has some affinities with P. serpens 
(Allman, 2: pp. 327-328; Pl. XI, figs. 7-9), but differs from it in the more slender 
hydrocauli and the more distinct difference between hydrocaulus and hydranth and 
in the adelocodonic gonophores. 
Sars (21: pp. 28-32; Pl. IL, figs. 37-43) has described a species from 
20-30 fathoms off Manger, Norway, which he named Rhizoragium roseum. This 
species appears to us to be so closely related to Perigonimus antareticus that it 
might with some propriety be placed in the same species. The reason for separating 
Rhizoragium roseum from the genus Perigonimus was undoubtedly the adelocodonic 
medusoid character of the gonophores, but in the character of the hydrosome it is 
undoubtedly a Perigonimus. 
Sars describes the ‘“ medusa-buds” as uncommonly large (up to 1 mm. in diam.) 
in proportion to the hydranths, the claviform naked part of which is only 0°3 — 
0°5 mm. in diameter. They are not attached to the naked part, but are situated 
on the creeping hydrorhiza as in P. muscoides. The degeneration of the gonophores 
consists in a reduction of the umbrella-wall and the loss of the radial canals and 
umbrella-mouth. In the oldest gonophores, however, the margin of the umbrella 
was thickened, and judging from the figure, it bore rudimentary tentacular processes. 
P. antarcticus resembles Rhizoragium roseum in many of these characters and 
also in the shapes and general characters of the hydranths and the number of their 
tentacles, but differs from it in the slightly branching habit of the hydrocauli and 
in having some of the gonophores arising near the proximal ends of the hydrocauli 
instead of only from the hydrorhiza. The gonophores of P. antarcticus are protected 
by a chitinous perisarc, but this is very thin, and may have been overlooked by Sars 
in his species. We have not found in our species any processes on the gonophores 
corresponding with the tentacular processes figured by Sars. However, in Rhizoragium 
the tentacular processes only occur in gonophores old enough to contain planulae 
larvae. In our species, on the other hand, the more mature gonophores exhibit a 
less well developed marginal thickening and in other respects the umbrella-wall is 
more degenerate than in the younger stages, and it therefore seems to us improbable 
that the tentacular processes would be present in stages old enough to contain larvae. 
Our conclusion is, therefore, that it is more convenient to regard Rhizoragium 
rosewum—which should in our opinion be called Perigonimus roseus—and Perigonimus 
antarcticus as distinct species, 
