i 7 8 DISCOVERY REPORTS 



Distribution. Prevously recorded by the National Antarctic Expedition and the Norwegian 

 Antarctic Expedition from South Georgia and by the ' Terra Nova ' Expedition from the Ross Sea. 



This species was taken in company with A. maxima at nine out of the twelve stations at which it 

 occurred. The greatest depth at which it was taken was 750-500 m. at station 376 in the South 

 Shetlands and the least depth was 60-160 m. at station 154 off Cumberland Bay. It only occurred 

 once in a night haul, at station 41 E off South Georgia. 



Genus Arthromysis Colosi, 1924 

 1924 Arthromysis Colosi, p. 3. 



Remarks. Cunningham (1871, p. 497) instituted a new species, Macromysis magellanica, for a few 

 specimens taken at the eastern end of the Strait of Magellan in January 1867. He gave a brief de- 

 scription of this species, stating that it resembled a species then known as Macromysis gracilis Dana 

 ( = Mysidium gracilis (Dana)) in general form, shape of the anterior end, and in having a deeply cleft 

 telson, but he gave no figures. 



Zimmer (191 5 b, p. 170) recorded very briefly a single damaged specimen taken in the Strait of 

 Magellan in 1892. He believed that this specimen represented a new species of the genus Antarcto- 

 mysis Coutiere, 1906, but felt that it was too damaged to allow him to institute a species for it. He 

 recorded that the main point of distinction between it and the known species of Antarctomysis was 

 the great length and slenderness of the eyes. 



Colosi (1924, p. 3) founded a new genus and species, Arthromysis chierchiae, for a single adult 

 female taken in the Strait of Magellan in 1882. He gave a fairly full description of it and figured the 

 anterior end, the telson and the distal end of an endopod of one of the thoracic limbs. 



Among the material collected by 'William Scoresby', I am fortunate in finding a number of 

 beautifully preserved adults of both sexes of this interesting species, taken at stations WS 89, off 

 Tierra del Fuego and WS 749, in the Strait of Magellan. From an examination of these specimens 

 I have no doubt at all that the species described by Cunningham, Zimmer and Colosi are synonymous. 

 I am now able for the first time to examine and to figure the male pleopods. From their form there 

 is no doubt that these specimens cannot be included in the genus Antarctomysis. I therefore accept 

 Colosi's genus Arthromysis for them, but the specific name chierchiae must give place to the earlier 

 name of magellanica. 



The definition of the genus Arthromysis can now be given more fully : Anterior margin of carapace 

 a smoothly rounded semicircle ; antennal scale long, setose all round, lanceolate, with narrowly rounded 

 apex, small distal suture. Eyes extremely long and narrow. Mandibular palp long and robust, second 

 segment long and narrow with parallel sides ; third segment much narrower and half as long as the 

 second. Endopods of the third to the seventh thoracic appendages with the carpo-propodus subdivided 

 into a large number of segments; that of the eighth divided into about half as many sub-segments; no 

 nail. Pleopods of the female reduced to simple unsegmented plates ; of the male, first and second pairs 

 almost exactly like the corresponding pairs of the female ; third pair, small, biramous, with normal 

 exopod ; endopod reduced to a simple unsegmented plate ; fourth pair biramous with the exopod 

 extremely long, multiarticulate, distal segments armed with very long modified setae; endopod re- 

 duced to a simple unsegmented plate ; fift h pair large, biramous, both rami normal, multi-articulate 

 and natatory; exopod slightly longer than endopod. Uropods with exopod considerably longer than 

 endopod; inner margin of endopod armed with a row of spines. Telson broadly oblong; deeply cleft; 

 lateral margins armed with a continuous row of almost equal spines not arranged in series ; pair of 

 long, plumose setae at base of cleft. 



