52 DISCOVERY REPORTS 



lo radial canals are retained, they are broad and flat, with female gonads 9 mm. in length, situated 

 about equi-distant from the stomach and the ring-canal, and containing large eggs. There are about 

 70 tentacles of very different sizes. Some few statocysts are retained. 



In a small specimen from St. 925, 10 mm. in diameter, the stomach is 2-5 mm. wide, the mouth 

 opening i-8 mm. ; it has 16 radial canals, but the tentacles could not be counted. In another specimen, 

 from St. 1606, 30 mm. in diameter, the stomach is 9 mm., the mouth opening 5 mm.; there are 

 16 radial canals and about 54 tentacles. 



Bigelow (1909) found three specimens of this species in the tropical East Pacific, but only one of 

 them was in a fairly good condition, 55 mm. wide with 33 radial canals and about 70 tentacles. Two 

 other species have been described: H. valdiviae was described, but not figured, by Vanhoffen (19120, 

 p. 384), several specimens being taken in the tropical parts of the Atlantic and Indian Oceans. Accord- 

 ing to the author, the species is distinguished from H. maasi by the number of radial canals which 

 do not exceed 16, in so far as it was possible to count them. As mentioned above, the specimens in 

 the Discovery collection, up to 40 mm. in diameter, have 16-20 radial canals. The number of tentacles 

 in H. valdiviae varies as follows : 



Specimens less than 44 mm. wide thus vary approximately within the same limits as the Discovery 

 specimens of corresponding size ; I therefore believe that they belong to the same species, and that 

 none of them differ so much from H. maasi that a specific separation seems reasonable. The largest 

 specimen observed by Vanhoffen, 70 mm. wide, had 204 tentacles; this very large number may per- 

 haps justify the erection of a separate species. Provisionally, therefore, I think we may retain the 

 name H. valdiviae for this single specimen, whereas all the others undoubtedly belong to H. maasi. 



My description of H. medius (Kramp 1948Z), p. 7, fig. i) was based on a specimen taken by the 

 Swedish Antarctic Expedition 1901-3, north-west of South Georgia; it was about 100 mm. in dia- 

 meter with 30 radial canals and about 280 tentacles. There is the possibility, of course, that H. maasi, 

 during continued growth, may produce this very large number of tentacles, though such an enormous 

 increase does not seem very probable. Until further evidence is available, it therefore seems to me 

 that we should retain H. medius as a separate species.^ 



Distribution. Tropical and antiboreal parts of the Atlantic, Indian and Pacific Oceans, mainly 

 south of the equator, in the deep and intermediate layers. 



Family RhopalonematIDAE 



Rhopalonema velatum Gegenbaur 1856 



Occurrence: Stns 68, 69, 89, 100, 102, 247, 250, 254, 256, 273, 282, 671, 672, 673, 674, 675, 676, 677, 678, 679, 680, 

 681, 682, 683, 685, 686, 687, 688, 689, 690, 691, 692, 698, 699, 702, 703, 704, 705, 707, 708, 709, 710, 712, 714, 

 718, 847, 963, 1370, 1371, 1372, 1373, 1374, 1375, 1568, 1571, 1573, 1574, 1575, 1576, 1581, 1585, 1586, 1587, 

 1749, 1770. (For details of station positions, date, etc., see Table i, p. no.) 



All the localities are within areas from which the species was known before. 



With very few exceptions the medusae were taken in hauls passing through the upper water-layers; 

 the only exceptions are at Stns 847 (N 100 B 270-196 m.) and 1575 (TYPE 800-550 m.). 



The following species are synonyms of R. velatum : clavigerum, coeruleum and polydactylum, all 

 described by Haeckel 1879, and R. striatum Maas 1893. Rhopalonema funer avium Vanhoffen 19026 is 

 a distinct species. 



1 Since the above was written, I have seen numerous specimens of Halitrephes collected by 'Dana', and I am now 

 convinced that H. maasi is the only existing species of the genus. 



