REPORT ON THE ISOPODA. 19 



The number of species known, therefore, which can be regarded as distinct, are four, 

 viz., Jsera albifrons, Jsera nordmanni, J sera wakishiana, and Jsera pubescens. 



A single species which I refer to this genus is described below; it appears to be 

 identical with Jsera pubescens, and differs from those already known principally in the 

 form of the uropoda, which are not so rudimentary as in Jsera albifrons, See. 



Jssra pubescens, Dana (PL II. figs. 6-10). 



Jam pubescens, Dana, Crustacea, U.S. Explor. Exped., pt. ii. p. 744. 



A large number of specimens of a Sphasrornid, which I identify with Sphseroma 

 gigas, were collected in rock pools at Kerguelen ; upon several of these were a number 

 of a minute species of Isopod living in a semiparasitic condition, which I identify with 

 Dana's Jsera pubescens. The occurrence of this species at Kerguelen was noted first 

 by S. I. Smith. 1 Dana's specimens were from Patagonia ; this species like its host and a 

 number of other species is common to Patagonia and Kerguelen. Dana's specimens 

 were obtained from Sphseroma lanceolatum, a Sphasromid which hardly differs 

 specifically from Sphseroma gigas. 



The general outline of the body is oval ; the body gradually increases in breadth up to 

 the third segment of the thorax, and thence hardly decreases until the abdominal shield 

 is reached. 



The head is roughly quadrangular, broader than long, with a short blunt rostrum. 

 The eyes are placed some way from the lateral margin of the head ; they are small and 

 each consists of two elements only — two crystalline cones (fig. 7), and two only are 

 plainly visible. 



The first segment of the thorax is rather longer, although narrower, than the 

 two following, which are subequal, the fourth is shorter again. The lateral margins of 

 the segments are rounded, the second to the fourth being somewhat bilobed ; the 

 anterior lobe is fringed with short hairs which are wanting posteriorly. 



The abdominal shield is rounded, with a slightly pointed obtuse termination, its 

 lateral margins are fringed with short hairs. 



The antennules (fig. 8) consist of a large oval basal joint followed by a more slender 

 and shorter joint, then come two shorter joints which are subequal ; the flagellum consists 

 of only two joints, of which the first is the largest ; they are both furnished with sensory 

 filaments. 



The antennas (fig. 9) are about half the length of the body ; the flagellum is very 

 considerably longer than the peduncle, and consists of about twenty joints ; in the 

 peduncle the first three joints are very short, the fourth longer, the fifth longer 

 again but narrower. 



1 Bull. U.S. Nat. Mus., No. 3, p. 63, 1876. 



