MYSIDACEA AND EUPHAUSIACEA 201 



Mysidacea 



The 'Terra Nova' 1 collected seven species of Mysidacea from South Georgia: 

 Pseudomma armatum, P. sarsii, Mysidetes posthon, Antarctomysis maxima, A. ohlinii, 

 Encopia atist ralis and Daclylamblyops antarctica. The Swedish Antarctic Expedition 2 

 had already collected Mysidetes posthon and the two species of Antarctomysis . More 

 recently Rustad (1930a) has retaken the first five, all from stations within Cumberland 

 Bay, and with the exception of one station he took them all in the deepest of his series 

 of three, four, or five vertical hauls. 



All the specimens collected in the N 100 H nets in the survey round South Georgia, 

 the nearest stations to land being 5 miles off the coast, proved to be of the single species 

 Antarctomysis maxima, Holt and Tatt. The specimens of Mysidacea taken in the N 70 V 

 nets, and recorded in Appendix II, have not yet been determined, and it is likely that 

 other species are present in the samples taken near the bottom. 



A. maxima was confined to the waters above the continental shelf of South Georgia. 

 During the December-January survey of 1926-7 it was abundant off the south-west 

 coast, being spread over the wide shelf on that side; it was scarce to the north-west and 

 south-east and all but absent from the north-east coast. Thus it had a distribution directly 

 opposite to that of the Euphausiids, particularly that of Euphausia superba, as will be seen 

 by comparing Fig. 88 with Fig. 92. This distribution is particularly interesting in 

 relation to the hypothesis of animal exclusion and in relation to this it will be further 

 discussed in a later part on p. 303. A complete record of its occurrence is given in 

 Appendix II. Sometimes, particularly in the hours of darkness, it occurred in large 

 numbers in the mid-water net of the series of three, but only occasionally and in small 

 numbers did it occur at the surface. 



Antarctomysis maxima is circumpolar in distribution ; it has been taken by the 

 Belgica, 3 Swedish Antarctic, 2 National Antarctic (Discovery), 4 Francaise, 5 Terra Nova 1 

 and Aurora 6 Expeditions. 



Euphausiacea 



The Euphausiacea form a very prominent feature of the plankton of the area and are 

 represented by six species of the genus Euphausia, and two species of Thysanoessa. 



The N 100 H nets proved to be the most efficient nets for sampling the Euphausiacea. 

 Unfortunately, these nets were not used at the four stations approaching South Georgia 

 from the north-east in February 1926. Under the heading of each species we will de- 

 scribe its occurrence in the different regions within the area, omitting reference to the 

 February 1926 line just mentioned unless the species was taken in the N 70 V nets 

 there used. 



Euphausia frigida, Hansen. This cold-water form, both in the adult and larval stages, 

 was well represented in our collections round South Georgia. Before discussing its 

 distribution it is necessary to draw attention to the remarkable diurnal vertical migration 

 1 Tattersall (1923). 2 Hansen (1913, 1921). 3 Hansen (1908). 



4 Tattersall (1908). 5 Coutiere (1906, 1917). 6 Tattersall (1918). 



