REPORT ON THE ISOPODA. 23 



The three succeeding segments of the thorax are subequal, the first alone being 

 slightly shorter than the two following ; the breadth of all these segments is equal and 

 a trifle greater than that of the head. The antero-lateral margins of these segments are 

 directed forwards and terminate in a short sharp spine ; the postero-lateral margin 

 is parallel to the antero-lateral, both being bent forwards at an angle to the transverse 

 axis of the seo-ment. 



The fourth segment of the thorax is shorter than any of the preceding, 

 it is considerably wider laterally than dorsally, owing to the fact that its postero- 

 lateral margin is directed backwards ; it forms, in fact, the transition between 

 the forwardly directed anterior and the backwarclly directed posterior segments; 

 its antero-lateral extremity, as in the case of the preceding ones, is furnished 

 with a spine. 



The three posterior segments of the thorax become successively narrower but longer ; 

 they are directed backwards instead of forwards and have no antero-lateral spines ; the 

 anterior margin of the fifth segment is closely applied to the posterior margin of the 

 fourth, the others are separated by considerable lateral incisions, as are the anterior 

 segments of the thorax. These incisions are, however, far less conspicuous than in such 

 genera as Pleurogonium. 



The abdominal segments are all fused together to form a single piece, which is about 

 as long as the two last segments of the thorax ; it is oval in form but wider anteriorly 

 than posteriorly ; between the uropoda the caudal shield is prolonged into a short spiny 

 median process. 



There is no trace of any segment intercalated between the last segment of the 

 thorax and the abdominal shield. The margins of the abdomen appear to be fringed 

 with slender hairs. The whole surface of the body, both dorsally and ventrally, is quite 

 smooth and free from tubercles or spines of any description. The median dorsal region 

 of the body is regularly convex, the lateral regions 'somewhat depressed. 



The antennules (PI. I. fig. 2) are about as long as the head and first two segments 

 of the thorax together ; the first joint of the peduncle is rounded and rather short and 

 broad, the second is longer but narrower, the third is shorter and narrower again, and 

 the terminal joint of the peduncle is very small indeed. The flagellum consists of about 

 fifteen joints, and extends a little beyond the commencement of the distal joint of the 

 antennary peduncle. 



The antennse (see fig. 3) are about equal in length to the body ; the flagellum is 

 rather longer than the peduncle. 



The two basal joints of the peduncle are extremely short, the third a trifle longer, 

 with an articulated scale on the outer side. 



The mandibles and maxillas I am unable to describe, as they were concealed by the 

 subjacent maxillepedes. 



