DESCRIPTION OF SPECIES 309 



in Richardson's Isopods of North America (1905) agree with my own observations, and 

 for this reason I include here a revised account of the species. 



Description. The body of the female is broadly ovate with a pronounced median 

 dorsal carina: the coxal plates are much flattened. The male is slightly broader in 

 proportion to its length than the female, and measures 8 mm. in length and 7 mm. 

 in greatest width; the female is only 5-5 mm. long and 4-25 mm. wide. 



The head is about as broad as long, with the anterior margin excavated on either side 

 of a small median rostrum for the reception of the antennules. Just within the anterior 

 margin, and running parallel with it, is a shallow transverse groove, behind which the 

 area of the head between the eyes becomes raised. The central portion of this area, 

 which is separated from the postero-lateral parts by slight grooves, is somewhat tri- 

 angular in shape, with the apex directed backwards and terminating in a small spiniform 

 process at the posterior margin of the head. At about the level of the middle of the eyes 

 this area is raised to form a second small median process. The eyes, which are situated in 

 postero-lateral positions on the head, are comparatively large, reniform in shape (not 

 oval as stated by Richardson) and contain black pigment. 



The lateral portion of the second thoracic somite, which is fused with the head, is 

 broad and flattened, without any transverse ridges. The third, fourth and fifth thoracic 

 somites are sub-equal, with the median keel produced backwards as a short spine; the 

 sixth and seventh somites are short, their length together equal to less than that of those 

 preceding them. Coxal plates well developed ; those of the third to fifth somites marked 

 oif by distinct sutures, and not "perfectly coalesced, with no indication of the place of 

 fusion" (Richardson, 1905, p. 322). Those of the seventh somite are produced back- 

 wards, but do not reach as far as the level of the base of the uropoda. 



The abdomen is composed of three free somites and a large terminal one. Each of the 

 free somites is keeled and bears a short median spiniform process. The process on the 

 third segment is not on the posterior margin, but on a well-marked transverse ridge 

 which extends across the segment, disappearing laterally on the pleural plates: this 

 ridge lies a short distance within the posterior margin. The pleural plates of the second 

 and third abdominal segments do not extend beyond the anterior margin of the terminal 

 segment ; those of the third segment are slightly the longer. The terminal segment is 

 large, somewhat triangular in shape. In the female the apex is obtusely rounded, but not 

 nearly as truncate as shown in Richardson's figure (1905, p. 321, fig. 353). In the male 

 specimen in my possession the distal extremity is broader than that of the female and is 

 slightly concave. A median and two lateral carinae are present ; each of the latter runs 

 parallel, one on either side, with the lateral margin of the segment, but at some distance 

 within it, meeting the median carina at its posterior extremity. 



The sterna of the three free abdominal segments are produced backwards to form 

 median spines ; in the female that of the first segment is much longer than those of the 

 other two, extending almost to the tip of the second ; in the male they are all of ap- 

 proximately equal size. 



In the antennule the first peduncular joint is broad, rounded and geniculate; the 



