EEPOJRT ON THE ISOPODA. 85 



Station 302, south-east of Valparaiso, December 28, 1875 ; lat. 42° 43' S., long. 

 82° 11' W. ; depth, 1450 fathoms; bottom temperature, 35° - 6 F. ; Globigerina ooze. 



Family Arcturid^e. 



Arcturus, Latreille. 

 Arcturus, Latreille, Le Eegne Animal, 1829, t. iv. p. 139. 



It appears to me to be quite necessarj^ to separate Arcturus and Astacilla. It is 

 true that the very remarkable elongation of the fourth segment of the thorax in Astacilla 

 is an adult condition not met with in the young, as the Rev, T. R. R. Stebbing has pointed 

 out. This is no reason, however, for uniting together the two genera, which differ also in 

 other characters, particularly in the brood cavity which is formed by four pairs of lamellae 

 in Arcturus, and by only one pair developed upon the fourth segment of the body in 

 Astacilla. I may also point out another difference, and that is in the hinder thoracic 

 limbs, which are biunguiculate in Astacilla and uniunguiculate in Arcturus; as this 

 character is evidently of importance in discriminating the genera of Asellidse it probably 

 should not be ignored in the present case. 



The genus Arcturus as thus limited is known by only four species exclusive of those 

 to be described in the present Report ; these are Arcturus baffini, Arcturus hystrix and 

 Arcturus tuberosus, from the Arctic region, and Arcturus co'p'pingeri from Patagonia. To 

 these I am able to add ten new species, most of which are from deep water. Three of 

 the above mentioned species, viz., Arcturus hystrix, Arctura tuberosus, and Arcturus 

 baffini, range into deep water, and the genus so far as it is known at present is 

 characteristically a deep-sea genus. 



Arcturus furcatus, Studer (PL XXV. figs. 6, 7). 



Arcturus furcatus, Studer, Sitzrmgsb. d. Ges. Naturf. Freuncle, Berlin, 1882, p. 57. 



The present species has been fully described and figured * by Professor Studer, from 

 examples obtained at Kerguelen by the German steam ship " Gazelle." The Challenger 

 acquired a very large number of specimens from shallow water up to 120 fathoms at 

 various localities at Kerguelen, and also further to the south, off Heard Island. In 

 addition to these specimens from shallow water a single specimen was dredged from 

 deep water (1675 fathoms), at the southernmost station, Station 158, close to the 

 Antarctic ice barrier, and this appears to be identical with Arcturus furcatus. The 

 occurrence of the same species in deep and in shallow water is most unusual (see p. 158). 



Although Professor Studer has defined the characters of this species with great accuracy, 



I think it worth while to give a short recapitulation in order to compare it with other species. 



1 Isopoden gesammelt wahrend der Reise S.M.S. " Gazelle," &c, Abhcmdl. d. h. Alcad. d. Wiss. Berlin, 1885, p. 12 

 (of Memoir), pi. i. fig. 3. 



