no. 1701. NORTHWEST PACIFIC ISOPODS— RICHARDSON. 



99 



The first three segments of the thorax are subequal in length, 

 being each about 1 \ mm. long ; the fourth segment is but little longer 

 than these, being only 1 J mm. in length ; the last three segments are 

 subequal and each is 1 mm. long. The anterior part of the lateral 

 margin of the second, third, and fourth segments is produced on 

 either side in a small lobe ; lateral to this lobe is the epimeron, which 

 is in the form of a narrow plate, gradually increasing in size. On 

 the last three segments the epimera are in the form of large, angular 

 processes extending laterally on either side of the segment and oc- 

 cupying one-half the lateral margin in the fifth segment, two-thirds 

 of the lateral margin in the sixth segment, and nearly all of the 

 lateral margin in the seventh segment, 



The abdomen is composed of three segments, two short ones an- 

 terior to the terminal segment. At the base of the terminal segment 

 are two lateral projections, one on either side, which, together with 

 the depression which extends across the segment, mark the place of 

 coalescence of another segment. The terminal segment is produced 

 to a bifid extremity ; it is 2^ mm. wide and 4 mm. long. 



There are four pairs of incubatory plates. a 



The first four pairs of legs are directed forward and are furnished 

 with long hairs ; the last three pairs are ambulatory. 



Five specimens, males and females (the female is described and 

 figured) were collected at station 4803, on the way from Milne Bay, 

 Simushir Island, Kuril Islands, to Hakodate, Hokkaido, Japan, by 

 the Boussole Strait at Cape Eollin, Simushir Island, N. 59° W., 

 9 miles (lat. 46° 42' N.; long. 151° 45' E.), and at station 4804, at 

 N. 58° W., 9.7 miles (lat. 46° 42' K; long. 151° 47' E.), at a depth 

 of 229 fathoms in coarse pebbles and black sand. 



This species is close to Arcturus heringanus Benedict,^ but differs 

 in the rugose and tuberculate character of the body, in the shorter 

 fourth thoracic segment and in the shorter abdomen, the apex of the 

 terminal segment not being produced as in A. heringanus. 



Type-specimen.— Cat. no. 39509, U.S.N.M. 



ARCTURUS HASTIGER, new species. 



Body narrow, elongate, 8J mm. : 52 mm. Surface minutely granu- 

 late. Head deeply excavate in the middle, with a small median 

 point. Antero-lateral angles acutely produced. Eyes very large, 

 composite, about twice as wide as long, transversely oval. Two 

 tubercles, one on either side of the median line, are situated about 

 the middle of the head between the eyes. The first pair of antennae 



° In the genus Arcturus there are four pairs of incubatory plates and not 

 three, as I have heretofore stated. The first pair are small and somewhat 

 obscured by the overlapping second pair. 



6 Proc. Biol. Soc, Washington, vol. 12, 1898, pp. 4&-47. 



