NO. 1788. NORTH AMERICAN ERGASILIDJE— WILSON. 335 



evenly rounded, sometimes forming a half circle. Second joint pro- 

 jecting on its anterior margin, and abruptly narrowed just beyond 

 its center to furnish the articulation for the third joint. 



The latter is as long as the two basal joints, but only one-quarter 

 as wide, narrowed near its proximal end, widened at the distal end, 

 and armed with a small rounded knob on its inner margin. Terminal 

 joint a claw, with a curved outer margin and a nearly straight inner 

 margin, the latter with one or two short teeth near its proximal end. 



The structure of these antennae is thus very different from that in 

 centrarchidarum and versicolor and furnishes a good specific chara.cter. 



Mouth-parts resembling those of centrarchidarum more than those 

 of versicolor, but quite distinct from either. Mandibles so short that 

 they hardly meet at the mid-line, with the knob on the anterior margin 

 of the basal joint prominent and well rounded as in centrarcJiidarum. 

 But the terminal joint is hardly longer than the narrowed portion of 

 the basal joint, tapers rapidly to an acute point, and is armed with 

 setae along its inner margin only. The palp also is attached farther 

 back on the basal joint than in other species; it is very narrow, almost 

 hnear in fact, one-fourth longer than the terminal joint, six times as 

 long as wide, and armed with minute tooth-like setae on its anterior 

 margin only. 



The first maxillae are similar to those in other species, but are 

 armed with shorter setae. The second maxillae resemble those of 

 centrarchidarum, but are shorter, acutely pointed at the tips, and 

 with a sharper curve near the base. 



Behind these second maxillae can be distinctly seen on the ventral 

 surface a set of chitin ribs for the attachment of the maxillipeds, but 

 the appendages themselves are lacking, as in all the females of this 

 genus. 



The presence of these ribs, however, proves conclusively that it is 

 a pair of mouth-parts corresponding to the maxillipeds in the male 

 which have disappeared, and thus adds one more convincing testi- 

 mony to the correctness of this interpretation of the mouth-parts. 



The swimming legs are similar to those in other species, all biramose 

 and the rami three-jointed, except the exopods of the fourth pair, 

 which have but two joints. The following is the arrangement of the 

 spines and setae: First exopod, I-O; 0-1; II-5: endopod, 0-1; 0-1; 

 0-5: second exopod, 0-1; I-l ; 0-5: endopod, 0-1; 0-2; 0-5: third 

 exopod, 0-1; 0-1; 0-5: endopod, 0-1; 0-2; 0-4: fourth exopod, 

 I-l; 0-5: endopod, I-l; 0-2-; 0-4. Fifth legs reduced to a pair of 

 long spines. 



Total length 0.8 mm. Carapace 0.5 mm. long, 0.25 mm. wide. 

 Length of free thorax 0.18 mm. Length of egg-strings 0.55 mm. 



Color a transparent horn color, the ovaries opaque but not as white 

 as in centrarchidarum. A large spot over the eye on the dorsal surface 



