62 THE VOYAGE OF H.M.S. CHALLENGER. 



ance of being shorter than they really are ; the fourth and fifth as well as the three 

 anterior epimera are separated from the terga by a distinct suture. The antero-posterior 

 diameter of the three anterior free thoracic segments gradually increases from the first 

 to the third ; the diameter of the fourth and fifth is rather more than half that of the 

 third. The sterna of the two first thoracic segments are as usual divided by lines of 

 suture into three portions ; the median sclerite of the first segment is keeled, and that of 

 the second segment has a median keel which bifurcates posteriorly; the hinder half of this 

 sclerite is divided by a median suture continuous with that which separates the right and 

 left halves of the sterna of the succeeding segments. As in Serolls hromleyana and Serolis 

 neosra, the median portions of the sterna of the last three thoracic appendages are fused, 

 though the lines of division corresponding to the three segments are more strongly 

 marked in this species than in the two above mentioned. 



Ahdomen. — The epimera of the abdominal segments have been already described 

 (cmtc, p. 13) ; the sterna do not appear to differ in the two sexes. The caudal shield is 

 squarish in outline, 7 mm. in length by 8 mm. in breadth ; its length is therefore not 

 (|uite one-third of that of the whole body. The uropoda are attached close to its posterior 

 margin. There is a slight longitudinal median keel, which is crossed at right angles by 

 a sinuous ridge with three convexities, one median and two lateral, which correspond 

 to the spines on the caudal shield of Serolis necBra and Serolis schythei ; at about the 

 end of the anterior third of the caudal shield is a sliort flat spine in the middle line and 

 two oblique ridges, one on either side of this spine ; the lateral portions of the caudal 

 shield are bent down. 



The two pairs of anteunce. are of about equal length. In the anterior pair 

 the first joint is short and oval ; the second joint is a little longer, and the upper 

 margin projects a little way beyond the articulation of the succeeding joint, which is 

 nearly twice its length, narrow, and bent downwards. The filament has fourteen 

 joints. 



The two distal joints of the basal portion in the second antenna3 are furnished with 

 hairs arranged in tufts along the upper margin. The filament has twelve joints. 



In the maxillipedes (PI. III. fig. 10) the stipes and lamina are not separated by a 

 complete suture ; the second joint of the palp has a small tubercle near the base covered 

 with hairs as in the other deep-sea species. 



The third thoracic appendages in the male resemble those of Serolis necBra in that the 

 inner margin of the third and fourth joints bears a number of delicate plumose hairs ; 

 a few are also to be found at the upper extremity of the second joint ; the penultimate 

 joint is swollen and considerably broader at the base ; the inner margin has about a dozen 

 pairs of conical papilla-like spines which grow longer and narrower towards the distal 

 extremity, where they come to resemble exactly the plumose hairs upon the anterior 

 j oints. 



