58 THE VOYAGE OF H.M.S CHALLENGER. 



cesses which are hollow and filled up with counective tissue, two smaller median 

 spines and two outer ones with a bifid extremity ; the posterior margin of the cephalic 

 shield is indented, and forms three projections, the two outer ones being somewhat 

 triancfular in shape, and tuberculated on the free margin, while the inner median one is 

 transversely elongated, and much like the labium in shape, with a slightly convex outer 

 margin. 



Thorax. — Each of the thoracic segments is furnished with a median spine — the first 

 three are considerably longer than the rest ; the antero-posterior diameter of the thoracic 

 segments increases from the first to the fourth, the latter measuring 3 "5 mm. in the male; 

 the two last thoracic segments are comparatively longer than in Serolis bromleyana, 

 rather more than half as long as the preceding segment. The terga of the three anterior 

 free thoracic segments are separated from their epimera by a distinct suture. The epimera 

 of the segments gradually increase in length up to the sixth pair, which are extremely 

 lono-, measuring 37 mm. in the male, and extend backwards in a direction nearly parallel 

 to the long axis of the body. 



The first epimera are larger in the male than in the female {cf. figs. 1, 3); in the latter 

 the margin of the epimera passes at first abruptly backwards, and then curves outwards ; 

 the antero-lateral portion of the cephalic shield projects outwards beyond the commence- 

 ment of the epimeron for a short space, and ends in a truncated slightly notched extremity; 

 in the male the outer margin of the first pair of epimera is quite regular. The epimera 

 are divided into two halves by a longitudinal ridge. 



The sterna of the two anterior segments are as usual divided by sutures into three 

 sclerites ; the anterior segment is similar in shape to that of Serolis bromleyana ; the 

 median sclerite of the second segment is saddle-shaped as in the last mentioned species, 

 but instead of being smooth the anterior half is produced downwards into a triangular 

 process ; the posterior half is raised into two knobs, which are separated from each other 

 in the median ventral line by a suture. The three succeeding segments are divided by 

 a median suture which is continuous to the end of the thoracic segments. The sixth, 

 seventh, and eighth thoracic segments are entirely similar to those of Serolis. bromleyana 

 above described. 



Abdomen. — The epimera of the second abdominal segment extend for a space of 

 about equal to half its own length beyond the caudal shield ; they are not perceptibly 

 longer in the male. The epimera of the third segment are very short, and only extend 

 to about the commencement of the lateral margin of the caudal shield ; the length of these 

 epimera also does not diff'er in the two sexes. The posterior extremity of the first pair 

 of these epimera is notched as in Serolis bromleyana. The sterna of the three free 

 abdominal segments difi"er in the two sexes ; in the female the posterior margin of each 

 is produced into a short spine, the first being the largest and longest ; in the male the 

 last of the three segments only has a spine. 



