REPORT OX THE ISOPODA. 37 



2. Serolis convexa, Cunningham (PI. VI. figs. 9-15). 



SeroKs corjvexa, Cunningham, Crustacea, &c., of H.M.S. " Xassau," Trans. Linn. Soo. Lond., 



vol xxvii. p. 498, 1871. 

 Serolis convexa, Studer, Isopoden gesammelt, &c., Abbandl. d. k. Akad. d. Wiss. Berlin, 1882, p. 9 



(separat Abdriick). 



The Challeuger obtained only a single specimen of this species, from Port William, 

 Falkland Islands ; I have, however, had the opportunity of comparing it with four other 

 specimens in the British Museum which are the types. 



Prof. Cunningham's description {Joe. cif., p. 498) is as follows : — "Most nearly allied 

 in form to Serolis planus, Dana. Body very convex, much more so than in any other 

 species of the genus with which I am acquainted. A prominent carina along the mesial 

 line. Two last segments of pereion distinctly narrower than those which precede them. 

 Last segment of pleon more elongated than in Serolis planus, and possessing three well- 

 marked ridges — a median, interrupted in the middle, and two lateral, each terminating in 

 a sharp point. Eyes very prominent, and placed rather near to each other." 



Two specimens were obtained by Prof. Cunningham on the north coast of Fuegia. 



Prof. Studer has also published some notes upon this species in his account of the 

 Isopoda collected during the voyage of the " Gazelle," and he has pointed out that the 

 chief character by which Grube distinguished Serolis convexa from Serolis gaudichaudii, 

 viz., a tuft of hairs upon the antepenultimate joint of the second thoracic appendages, 

 is really a secondary sexual character peculiar to the males not only of Serolis convexa 

 but also of Serolis gaudichaudii ; before Prof. Studer's paper came into my hands I had 

 noted the same fact, and alluded to it briefly in my Preliminary Eeport;' the speci- 

 men dredged by the Challenger is a male, and it shows another character which I Ijclieve 

 to be peculiar to the males ; on the sterna of the last three thoracic segments is a small 

 patch about 2 mm. in length l.)y 1 mm. in breadth, distinguishable by its velvety appear- 

 ance and darker colour from the surrounding integument ; this on microscopic examina- 

 tion proved to be covered by a multitude of hairs exactly similar to those found upon the 

 second thoracic appendages, only rather shorter ; some of the segments in front also, 

 especially the second, have a small tuft of these hairs. 



In other respects the males and females of this species do not differ greatly in appear- 

 ance ; the males are imperceptibly broader in proportion to their length than the females, 

 as shown by the foUowdng measurement taken from the male in the Challenger collection 

 and the single female specimen in the British JMuseum : — 



Length. Breadth. 



Male, ....... 2.5 mm. 20 mm. 



Female, ....... 25 „ 19 „ 



The sterna of the ahdominal segments present no differences in the two sexes. 



1 Proc. Zool. Soc. Lond., pt. iii., 1884, p. 330. 



