. DISCOVERY REPORTS 



Neritic species of Leptolina (Table 2) 

 As Table 2 shows, not all the distributional regions are covered by the Discovery collections, and 

 the area most extensively investigated is the Atlantic Ocean, from which by far the most material 

 is available and to which the succeeding remarks mainly apply. 



In all, thirty-four species of neritic Leptolina have been taken by the Discovery Investigations— 

 these include the following new species : Russellia mirabilis from the Pacific and Atlantic sectors of 

 the Antarctic and later found also in West-Indian waters; Rathkea africana from tropical West Africa; 

 Leiickartiara annexa from South Africa and tropical East Africa; and Ectopleura sacculifera from the 



Pacific coast of Ecuador. 



Among the remaining thirty species, nine occur in Antarctic waters, and it is characteristic that at 

 least six of them are circumpolar. Eighteen species occur in the West-Atlantic-antiboreal region. 

 Two of them are bipolar, Halopsis ocellata and Staurophora mertensi, both of which are found in the 

 northern boreal region as well as in antiboreal waters near the Falkland Islands. Staurophora mertensi 

 also penetrates into the Antarctic as far south as the South Orkney Islands. Apart from 5. mertensi, 

 only three species are common to both the West-Atlantic-antiboreal and the Antarctic regions, 

 namely : Cosmetirella davisi, Bougainvillia macloviana and Tiaricodon coeruleus. This is very remarkable, 

 since, according to Ekman (1953, p. 349), 'Quite a number of (pelagic) species are common for both 

 this region (the antiboreal) and the antarctic, that is for the whole of the cold-water region of the 

 Southern Ocean.' As examples Ekman mentions some species of copepods, amphipods, and euphau- 

 siids; evidently this does not hold good as far as the epipelagic medusae are concerned (see also p. 98 

 under the epipelagic Trachylina). This impression is confirmed by the other medusae known from 

 the two regions but not collected by the Discovery Investigations ; among thirteen of these species 

 seven are purely antarctic, five occur in the West-Atlantic-antiboreal region (mainly at the Falkland 

 Islands), but are not recorded from antarctic waters, and only one is known from both regions. 



In the south-western Atlantic, the Antarctic Convergence evidently constitutes a fairly eflFective 

 barrier between the antarctic and antiboreal faunas of neritic medusae, very few species penetrating 

 from one of these regions to the other. The fauna of the West-Atlantic-antiboreal region, however, 

 is a mixture of different constituents. Several of its inhabitants are characteristic of the area, but there 

 is a considerable admixture of species belonging to tropical waters. Seven of the species shown in 

 Table 2 penetrate into the tropics, but nine are known from southern waters only. The influence of 

 the Brazil Current must account for this admixture of tropical species, some of which are distributed 

 northwards into the boreal parts of the Atlantic. The antiboreal region is thus sharply limited to the 

 south, but not to the north, the Subtropical Convergence (called the antiboreal by Ekman) being a 

 less restricting factor to these animals than is the Antarctic Convergence. 



Three of the antiboreal species appear to have a very restricted distribution between the Falkland 

 Islands and the neighbouring coast of South America; they are Aglauropsis conanti, Proboscidactyla 

 mutabilis and Laodicea pulchra. Bougainvillia macloviana} Tiaricodon coeruleus and Phialella falk- 

 landica have a scattered occurrence in the southern parts of the Indian and Pacific Oceans also, while 

 of particular interest is the appearance in the South African region (see pp. 4, 15, 30, 31) of the two 

 decidedly southern species, Sarsia gracilis and Halitholus intermedins, as well as of the two antarctic 

 species, Mitrocomella frigida and Cosmetirella davisi. 



Very few neritic Leptolina were collected by the Discovery Investigations in the tropical Atlantic 

 and they afford evidence of no particular interest, but the material from the South African region on 



' The occurrence of B. macloviana in the East-Atlantic-boreal region (the North Sea) is undoubtedly due to trans- 

 portation by ships. 



