EEPORT OX THE ISOPODA. 51 



abruptly at riglit angles, terminating a little way in front of the second transverse ridge. 

 The margins of all the epimera are minutely serrated externally. The terga of the free 

 thoracic segments have almost the same autero-posterior diameter, the two last being 

 only a trifle narrower ; the sterna of the first two thoracic segments are as usual divided 

 by sutures into a median and two lateral sclerites ; the median sclerite of the anterior 

 segment is keeled, that of the second has a short keel, widening behind and extending 

 over its anterior half only. The posterior margin is raised into a ridge, which is continued 

 along the lateral sclerites, but is here rather narrower. The sterna of the three last 

 segments are partly fused as in other species. 



Abdomen. — The caudal shield is rather more than one-third of the lencrth of the 



O 



whole body ; its shape is pentagonal, and the end is produced into a long spine ; there is 

 a distinct longitudinal keel, which is furnished with three to six short recurved spines, 

 the first of which is always the largest ; at the anterior end of the caudal shield are two 

 short spines, one on either side, and closely approximated to the middle line ; from the 

 outer margin of each of these runs a fold somewhat curved in its course, which terminates 

 a little in front of the attachment of the uropoda in a short spine ; this lateral fold is 

 similar to that found m. Se rolls paradoxa and Serolis schythei, and perhaps marks the 

 boundary of the last segment of the abdomen ; the lateral margins from the attachment 

 of the uropoda to the terminal spine are provided with a number of small teeth. 



On PI. I. are figures of a male (fig. 1), female (fig. 2), and an immature male 

 specimen (fig. 3); the latter is introduced in order to show its similarity in shape to the 

 female (see p. 27). 



The first pair of antenme are shorter than the second pair by about half their own 

 length ; the terminal joint of the base is large, being rather more than half as long as the 

 preceding joint; the filament, which is about as long as the rest of the antenna, has 

 twenty -five joints. 



In the second pair of antennae the basal portion has as usual five joints, of which the 

 last is the longest, being about equal in length to both the third and fourth joints 

 together. The filament is nearly but not quite as long as the fifth joint, and is composed 

 of fifteen or sixteen joints. One of these is shown highly. magnified in PI. I. fig. 6 ; 

 on the inner and lower surface of some of the joints towards the middle of the filament 

 is a row of short lancet-shaped spines; these decrease in size towards the distal end of the 

 filament, and in the last three or four joints seem to be entirely absent ; they commence 

 to be visible on about the third joint of the filament, but are only present in small 

 numbers towards the distal end of the joint and close to its articulation with the one in 

 front. The figure (PL I. fig. G) represents the seventh joint ; these spines, which are 

 present upon the antennae of both sexes, are like those that are found in Serolis paradoxa, 

 and which have been described (ante, p. 35). 



Mandibles. — The distal extremity of the right and left mandibles of a male specimen 



