DISTRIBUTION OF ANTARCTIC MACROPLANKTON 123 



remembered that these species never occur except in small numbers, and the mere 

 presence of one of them in a sample is of some significance. The moderately "cold" 

 species also (group (g)) are on the whole better represented in this survey than in the 

 others, Limacina helicina and Metridia being specially numerous. Of the warm-water 

 species Eucalamis, Candacia and the Chaetognatha are also strongly represented, but 

 Eaphausia triacantha, Calanus simillimus, Pleuromamma, Limacina balea, Pareuchaeta, 

 Parathemisto, and Euphansia frigida are all in comparatively small numbers. It can be 

 said in fact that in spite of the prominence of one or two warm-water species, this 

 November survey was characterized by a much "colder" plankton than any of the 

 other groups of stations. 



During the survey of 1928-9 taken in December and January three of the very coldest 

 group were present and the moderately "cold" species were well represented, notably 

 Salpa, Tomopteris and Clione. Of the warm-water species Candacia and Heterorhabdus 

 were absent, Euphausia triacantha and the Chaetognatha were scarce ; but there was an 

 increase in the number of Calanus simillimus, Pleuromamma, Limacina balea, Parathemisto 

 and Euphausia frigida, and Pareuchaeta was more numerous than at any other time. 



During the survey of 1929-30 in January and February only one of the coldest group 

 was taken, a single specimen of Vanadis at St. 336, and the other "cold" species were 

 very poorly represented. Of the warm-water species Euphausia triacantha, Calanus 

 simillimus, Pleuromamma, Parathemisto, and Euphausia frigida were more numerous than 

 at any other time (though it must be remembered that the plankton as a whole was very 

 abundant during this survey) and the Chaetognatha, Limacina balea, and Pareuchaeta 

 were also prominent. 



The survey of 1927-8 in February and March was also characterized by a warm-water 

 plankton. None of the ' ' coldest ' ' group was taken, and with the exception of Metridia the 

 moderately " cold " species were all scarce. Among the warm-water species the presence 

 of the sub-Antarctic species, Euphausia vallentini, is specially significant and although 

 the plankton as a whole was not very rich Heterorhabdus and Limacina balea here 

 reached their maxima and Calanus simillimus and Euphausia frigida were both relatively 

 numerous. 



At the stations taken in March 1 930-1 the plankton population was again of a colder 

 type, in which two of the very cold-water species are present and Pyrostephos, Metridia 

 and Salpa are strongly represented. There is support for the "warm" group, however, 

 in Pareuchaeta, Parathemisto and Euphausia frigida, whose numbers are large in pro- 

 portion to the total amount of plankton. 



At the stations taken in April 1928-9, hardly any colder water species were re- 

 presented. Of the warm-water species Eucalanus, Candacia and Heterorhabdus were 

 absent, but Calanus simillimus, Limacina balea and Parathemisto were present in quite 



large numbers. 



Finally on the winter survey of September 1928, although the temperature of the 

 water was below o° C. at all stations and colder than at any other group of stations 

 around South Georgia, none of the " coldest " species was taken and all the warm-water 



