..1686 NEW ISOPODS FROM THE PACIFIC OCEAN— RICHARDSON. 69 L 



The head is large and is surrounded anteriorly and laterally by a 

 wide marginal border or ridge. There are no eyes. The three divi- 

 sions of the body — the head, thorax, and abdomen — are well defined. 

 The segments of the thorax are also well marked, the coxal plates 

 occupying the lateral margins. There are six distinct segments, with 

 six pairs of coxal plates. The first segment is coalesced with the 

 head. The first coalesced segment bears the first pair of legs. The 

 following five segments bear each a pair of legs, so that altogether 

 there are six pairs of legs. The last free (sixth) segment bears a 

 pair of modified appendages. 0 



The abdomen is narrower than the thorax, and tapers to a rounded 

 extremity. It is unsegmented and is devoid of appendages. 



Fig. 2.— Holophryxus giardi. Immature female and host. 



Only one immature female was taken at Station 4793, Toporkov 

 Island, Harbor of Nikolski, Bering Island, north 58° east, 44 miles 

 (54° 48' north, 164° 54' east), at a depth of 2,700 fathoms. It was 

 attached to the dorsal surface of the carapace of the host, Gennadas 

 borealis Rathbun, with the head directed posteriorly. The photo- 

 graph (fig. 2) is of the immature female and its host. 



a They may be analogous to or homologous with the fifth pair of appendages 

 of Heterophryxus appendiculatas Sars. ( Challenger Report, XIII, 1885, Pt. 37, 

 pp. 220-221, pi. xxxviii,, figs. 8-14.) See Tattersall for description and figures 

 of this form. (Fisheries, Ireland, Sci. Invest., 1904, II, 1905, pp. 77-78, pi. xi, 

 figs. 1-4.) Or, this segment may be considered the first abdominal segment with 

 its appendages. 



