CETWINIA. 87 



the secondary branch has its two median joints very 

 short, and bears three terminal setse, each of the three 

 preceding joints bearing a single long plumose seta. The 

 biting extremity of the mandible (fig. 6) is broad and 

 strongly toothed, palp composed of a large basal 

 joint and two slender branches, one of which is 

 indistinctly 3-jointed; all these bear numerous long 

 plumose setse. The first pair of swimming feet 

 (fig. 10) is somewhat smaller than the following 

 pairs, and has both branches of nearly equal length, 

 the marginal spines are long and slender, the setge 

 short, and the first two joints narrowed at the bases. 

 The second pair (fig. 11) has the peduncle forming a 

 rounded process on the inner side (fig 2a) ; branches 

 subequal, with all the joints much narrowed at the 

 bases ; first joint of the inner branch (b) very large, 

 distally dilated, outer angle acute and slightly pro- 

 duced, inner forming two very long curved spinous 

 processes. Third pair (fig. 12) much like the second, 

 except that the inner branch is shorter, the bases of 

 the last two joints are not much narrowed, and the 

 first joint has only one large curved spine (c) ; the 

 fourth pair (fig. 13) has the inner branch very short, 

 the marginal spine of the first joint being reduced to a 

 curved bristle (d) ; the joints of the outer branch 

 are elongated and basally constricted. The fifth pair 

 were not observed, and are either entirely absent or 

 very small. Caudal segments slender, about five 

 times as long as broad, and equal in length to 

 the last two abdominal rings ; setae strongly plumose, 

 short, the longest about equal to the last four 



