EEPOET ON THE ISOPODA. 47 



5. Sei'olis sejitemcarinata, Miers (Pis., 11. fig. 14, VIII. figs. 3-5). 



Serolis quadricarinafa, "White, List Crust. Brit. Mus., 1847, p. 106. 

 Serolis sejdemcarinafa, Miers, Ann. and Mag. Nat. Hist., 1875, p. 116. 

 SeroUs sepiemcarinafa,^ Miers, Phil. Trans., 1879 (extra vol.), p. 206. 

 SeroJig oualig, StiiJer, Arohiv f. Naturgesoh., 1879, p. 21. 



That Serolis scptemcarinata is the same species as Serolis ovalis cannot be doubted ; 

 the descriptions and figures given l»y Miers and Studer agree in every detail. 



Both these observers described the species from a single specimen only ; Studer's 

 description relates to a female specimen from Kerguelen, while IMiers's specimen was 

 dredoed at the Crozets. 



The Challenger obtained this species at Kerguelen, and also off Prince Edward's 

 Island ; the species therefore is common to these three groups of Antarctic Islands, Intt 

 has not as yet been obtained elsewhere. 



Studer remarks the rarity of this species as compared with Serolis latifrons, and 

 suggests that the absence of the spine-like uropoda found in Serolis latifrons may render 

 it an easier prey to its enemies ; the Challenger, however, collected a large number of 

 specimens of this species at Kerguelen, very nearly as many as of Serolis latifrons. 



The males of this species difi'er from the females by their greater size. 



The largest male specimen measures 13 mm. in length by 11 mm. in lireadth, the 

 largest female specimen measures 11 mm. in length by 9 mm. in breadth. All the 

 specimens obtained by the Challengei; with the exception of a few newly hatched young, 

 are almost exactly the same size as the two specimens from which the measurements are 

 taken, and the superiority in size of the males over the females can therefore be very 

 plainly seen. 



The abdominal epimera are similar in both sexes. 



A noticeable difference between the two sexes is to be found in the first thoracic 

 epimera ; the under surface of these epimera in the males is furnished with a row of 

 ridge-like tubercles, six or seven on either side, which are situated just external to the 

 attachment of the appendages ; they are a,rranged in a semicircle, with the convexity 

 directed forwards and outwards ; in the female there is no trace of any such structure ; 

 it is probable that these tubercles assist the male in maintaining a firm hold of the female 

 during copulation. 



The general surface of the body, especially the ej^imera, is sculptured, the latter are 

 traversed by innumerable ridges anastomosing with each other ; on the cephalic shield 

 and the tergal portion of the segments the surface is covered by minute scattered pits. 

 All the epimera, with the exception of the first, are traversed by a crescentic ridge which 



' In my opinion the catalogue name Serolis quadrimrinata ought not to have heen changed by Jliers in spite of its 

 being a "nomen ine2Huiii," but since the actual description of the species is under the name of Serolis septemcarinata, it 

 is necessary to adopt it here. 



