EEPOET ON THE ISOPODA. 151 



uropoda ; in the female (fig. 7) the two rami are subequal ; in the male (fig. 6) the fixed 

 endopodite is rudimentary, and the exopodite is a long, curved, spine-like joint. It will 

 be noticed that this difference of sex, and in the present specimen it undoubtedly is 

 merely a difference of sex, represents what has been by many regarded as a generic dis- 

 tinction. 



Both specimens are of a pale light-brown colour ; the surface of the body is more or 

 less tubercular ; the general form of the body is characteristic of the genus, except 

 in its extreme flatness ; I have represented this in fig. 8, which is a lateral view of the 

 Crustacean. 



The head is rather short and is bounded in front by a prominent ridge, which projects 

 in the middle line as a short rostrum ; the eyes are rather small and rounded ; they are, 

 however, inconspicuous from their white colour. 



The first segment of the thorax is larger than any of the following ; the five following 

 segments are subequal and are furnished laterally with curved epimera ; the epimera of 

 the fourth segment are larger, and those of the last of these segments are more distinctly 

 hooked at their extremity than any of the foregoing. The sixth segment of the thorax 

 is of equal antero-posterior diameter with the preceding segments, its epimera are, how- 

 ever, rudimentary and do not extend nearly so far laterally as the epimera of the foregoing 

 and the following segments. 



The abdomen consists of four free segments and a caudal shield ; in the female I 

 could not observe more than three free abdominal segments ; the first and fourth segments 

 of the abdomen in the female are very short and rudimentary, and have no lateral 

 extension ; the two middle segments are distinct from each other dorsally, laterally they 

 are fused and project outwards in a large epimeron, which reaches as far as those of the 

 thoracic segments, but instead of being bke them, sickle-shaped with a curved anterior 

 and straight posterior margin, they are square in outline and truncated at the extremity. 

 The antero-lateral regions of the caudal shield are prolonged into epimera of a precisely 

 similar form; the caudal shield is triangular in outline, and has two prominent, blunt, 

 median tooth-like processes situated one behind the other. Inferiorly it is excavated 

 for the reception of the abdominal appendages, the excavation being surrounded by a 

 flattened rim. 



The antennules are of about equal length with the antennae but rather more slender ; 

 the peduncle has three joints and the joints increase progressively in length, they are 

 smooth; the flagellum is many-jointed and about equal in length to the peduncle. 



The antennse have a three-jointed peduncle; the basal joint is long and stout, the second 

 joint of equal diameter, but rather shorter ; the third joint is much more slender and 

 about equal in length to the second ; the flagellum is multiarticulate and shorter than the 

 peduncle. 



The abdominal appendages of the first five pairs have been referred to above (p. 147); 



