PYCNOGONIDA OF THE SCOTTISH NATIONAL ANTARCTIC EXPEDITION. 161 



C. brevicaudatum, Miers, only previously known from Kerguelen, now extends its 

 range to Scotia Bay. 



Ammothea. — Two individuals of a single species of this genus were found, and are 

 identified with Professor Bouvier's^I. communis, which was found in great numbers by 

 the Francais on the west side of Graham's Land. The members of this genus appear 

 to be abundant in the Magellan Province, but none were seen by the Discovery in 

 M'Murdo Sound. 



Leionymphon is a genus instituted by Professor Mobius for some immature 

 specimens found off Bouvet Island. The collection of the Discovery, which was rich in 

 these forms, necessitated a revision of the genus, which now includes no less than eight 

 species, a key to which is given in my report on that collection (13). The two species 

 included in the present collection were described many years ago by Dr G. Pfeffer, 

 under the generic name of Ammothea. They were then recorded from South Georgia, 

 and it is only to be expected that they should occur also in the South Orkneys. L. 

 grande, however, has had its range extended considerably, and evidently has a circumpolar 

 distribution. 



Colossendeis is represented by two individuals, two very distinct species claiming 

 them. One is a Challenger species, C. leptorhynchus, and was taken in the area where 

 it was first found. The other is introduced as new ; it is quite blind — not an unusual 

 character of the genus, but the more surprising as it is a shallow-water species. 



When considering geographical problems during our stay in the Antarctic regions, 

 I accepted the mean annual isotherm of 45° F. for the ocean surface, as defined by 

 Dr A. Buchan (4) in the concluding volume of the " Challenger " Reports, as the northern 

 limit of the Sub- Antarctic region, partly perhaps as a matter of convenience, and partly 

 because it is a natural limit which includes Kerguelen Island and its neighbours, which 

 have, for a long time, been regarded as " Antarctic," and which have become " classical ' 

 ground by the work of that expedition. The value of this boundary is emphasised by 

 the fact that Professor Pelseneer (23), when reporting on the Mollusca of the Belgica 

 Expedition, and examining the subject exhaustively, fixed on the isotherm of 40° F. for 

 the air in July, and a similar isotherm for the ocean surface, but a minimum and not a 

 mean temperature ; for this latter isotherm Sir John Murray is the authority. All 

 the three isotherms above quoted are in very close accord, and a little south of lat. 45° S. 

 on the Pacific side, a little above it on the side of the Atlantic and Indian Oceans. As 

 to the boundary between the Sub- Antarctic and the Antarctic regions, I suggested in 

 my report on the Pycnogonida of the Discovery that lat. 60° S. might be provision- 

 ally regarded as such ; it includes all the glaciated lands of the Antarctic continent and 

 the islands connected therewith. A more satisfactory limit would be the average limit 

 of pack ice, if a surface phenomenon is to be accepted ; otherwise the centre of the 

 trough between the Antarctic continent and the more northern lands would make a 

 natural division, but the position of this trough will for some time at least be a matter 

 of conjecture. 



