6 SYDNEY J. HICKSON and F. H. GEAVELY. 



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; PI. I., 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 

 (AUman, 2 : pp. 327-328 ; PI. XL, 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; PI. II., figs. 37-43) has described a species from 

 20-30 fathoms off Manger, Norway, which he named Rhizoragium roseuni. This 

 species appears to us to be so closely related to Perigonimus antarcticus 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 — 

 ■ 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 

 roseum — which should in our opinion be called Perigonimus roseus — and Perigonimus 

 antarcticus as distinct species. 



