loo DISCOVERY REPORTS 



the Mediterranean and is recorded from several localities in the antarctic region (see text-fig. 9, p. 57), 

 it must be very eurythermal. Arctapodema antarcticum, previously known only from near the Antarctic 

 Continent in about 90"^ E, was taken in four localities, St. 1718, off Knox Land, 64" 23' S, 106° 33' E, 

 900-550 m.; St. 1838, west of the South Sandwich Islands, 700-250 m.; and near the Shag Rocks, at 

 St. 1917, 1400-1000 m., and St. 1919, 1800-1300 m. The temperature of the deep layers was not 

 measured at any of these stations; it probably varied between 0-5° and 2-5''C. Accordingly this species 

 belongs to the ' warm deep water ' ; but it is not one of the cosmopolitan bathypelagic species penetrat- 

 ing southwards towards the antarctic shelf. 



The third species oi Arctapodema, A. australe, was not taken in the antarctic region by the Discovery 

 Investigations, but it was described from the Gauss Station and thus apparently belongs to the 

 antarctic fauna. It is of considerable interest that this species together with A. antarcticum was taken 

 much farther north in the Indian Ocean, about 32" S. Both were taken in deep water, A. antarcticum 

 at St. 1749, at 1050-600 m., A. australe at St. 1753, at 2900-1400 m. These stations are about mid- 

 way between South Africa and south-west Australia, above the northward continuation of the 

 Kerguelen-Gaussberg Ridge and the water-temperatures are in no way remarkable. In the series 

 of stations along a line in 32° S, the temperatures in the deep layers increased fairly evenly from 

 St. 1738 near Australia to St. 1762 and 1763 south of Madagascar, approximately as follows: 



There is no indication of particularly low temperatures at Stns 1750 and 1752 (there are no 

 measurements from Stns 1749 and 1753 where the two species were collected), which might explain 

 why these antarctic medusae were found just here. Nevertheless, their occurrence in this tract of the 

 deep water may indicate that the northward movement of the antarctic bottom water has been 

 especially strong along the ridge (cf. Deacon 1937, p. 97). 



The remaining nine species of bathypelagic Trachylina are widely distributed, most of them are 

 almost cosmopolitan in the deep water of the oceans. Crossota brunnea, however, occurs only in the 

 southern hemisphere; Haliscera conica occurs somewhat farther north in the Atlantic and in the 

 Mediterranean, but it has not been observed outside the Atlantic area except in the antarctic region, 

 where it is circumpolar. 



In contradistinction to the epipelagic Trachylina, most of the widely distributed bathypelagic species 

 penetrate into the antarctic region, but there are also some species which seem to avoid the southern 

 regions. All of them occur in the area around South Africa, most of them extending also into the 

 boreal parts of the Atlantic and Pacific Oceans. Five of these species, Crossota brunnea, Pantachogon 

 haeckeli, Haliscera conica, Halicreas minimum, and Botrynema brucei, penetrate into the antarctic 

 region (see Text-figs. 17-18). Probably all of them are circumpolar, but very few collections have been 

 made in the Pacific sector. The depths at which they were taken cannot be stated exactly but ranged 

 between about 700 and 2400 m., though mainly at more than 1000 m. below the surface. Accordingly 

 their occurrence in the antarctic region is restricted to the 'warm deep water'. One might perhaps 

 be inclined to anticipate a difference in their bathymetric distribution according to the distance from 

 the continental slope, but nothing is indicated by the available data. There is not much difference in the 

 southward distribution of the species. The range of temperature was between about 0-2° and i-8'^C. 

 In contradistinction to these preceding five species, Rhopalonema funerarimn, Colobonema sericeum, 

 Halitrephes maasi and Aeginura grimaldii do not approach the antarctic region (see text-fig. 19). All of 



