REPORT ON THE ISOPODA. 61 



9. SeroHs gracilis, F. E. B. (PL III. figs. 7-13). 



SeroUs gracilis, F. E. Beddard, Pioc. ZooL Soc. Lond., 1884, pt. iii. p. 332. 



Five specimens of this species were dredged at Station 120 (675 ftxthoms), three males 

 and two females. 



The males were approximately of the same size, the largest measuring 21 mm. iu 

 length by 22 mm. in breadth; the females were much smaller, measuring 9 mm. in length, 

 by 8 mm. in breadth. 



The chief difference between the two sexes, apart from that of size and relative 

 proportions of length and breadth, consists in the greater length of the epimera in the 

 males ; in the female specimens (PL IIL fig. 8) the last thoracic epimera hardly reach as 

 far as the end of the caudal shield, while the first abdominal epimera only extend about 

 haK way down, and the posterior abdominal epimera terminate at about the level of the 

 end of the anterior third of the caudal shield ; in the male (PL IIL fig. 7) the posterior 

 thoracic epimera are considerably longer, reaching beyond the caudal shield for a space 

 of about its own length; the actual length of these epimera is 13 mm.; the first 

 abdominal epimera extend a short way beyond the end of the caudal shield, and the 

 posterior pair to about the middle. The difference between the two sexes in the length 

 of the epimera is more marked in this species than in any other known to me. 



The general form of the body is circular, and the dorsal surface is covered with 

 scattered pits ; the colour (in alcohol) is a dark slate-blue, varying to reddish yellow upon 

 the terga of the posterior thoracic and abdominal segments. 



The cephaliG shield has much the same shape as in Serolis hromleyana ; the portion 

 l}T^ng between the eyes, which are small and inconspicuous, is strongly convex, while the 

 antero-lateral areas are flat and depressed, and do not rise above the level of the first 

 thoracic epimera ; a transverse ridge running from the base of the rostrum, which is very 

 minute, divides the cephalic shield as in Serolis hromleyana. 



TJiorax.- — The first epimera are divided into three portions by two transverse ridges ; 

 the anterior one is continuous with the ridge that traverses the cephalic shield, it passes 

 at first across the epimeron and then bends backwards running parallel with the anterior 

 margin of the epimeron, and joins the distal end of the second ridge ; the continuation 

 of these two ridges passes along the margin of the epimeron closely applied to it, and 

 terminates some way in front of the end of the epimeron. The posterior ridge corresponds 

 to the line of suture between the two fused epimera of the first and second thoracic 

 segments. 



The other epimera are fiat and sickle-shaped, not spinifonn as in Serolis hromleijana 

 and Serolis necera; they gradually increase in length up to the sixth; the articular 

 processes, which unite together the succeeding epimera, are placed further than is usual 

 from the junction between the terga and the epimera, which gives the latter the appear- 



