AKT. 5. NORTH AMERICAN PARASITIC COPEPODS WILSON. 41 



genital segment and the abdomen exposed in dorsal view. In mature 

 adults it is lengthened and broadly rounded, leaving only the anal 

 laminae visible dorsally. 



Genital segment twice as wide as long, with protruding, convex 

 lateral margins. Abdomen only half the width of the genital seg- 

 ment, narrowed anteriorly and with convex sides. Anal laminae 

 cylindrical, filiform, five times as long as wide, with bluntly rounded 

 tips, without setae. 



First antennae small and indistinctly segmented, apparently about 

 seven-Jointed, somewhat flattened antero-posteriorly and regularly 

 tapered, with tM'o tiny setae at the tip. Second antennae on the 

 ventral surface of the lateral flaps of the cephalothorax, consisting 

 of a stout basal joint and a curved terminal claw. First maxillae at 

 the sides of the mouth tube and very small; second pair long and 

 slender, with a short terminal claw, having a row of saw teeth along 

 each lateral margin. On the side of the terminal joint below the 

 base of the claw is a small spine. The maxillipeds, like the second 

 antennae, are made up of a stout basal joint and a curved terminal 

 claw, apparently jointed near the center. 



The exopod of the first legs is quadrangular, with five stout tri- 

 angular spines along the terminal margin ; the endopod is narrowed 

 to a thin neck where it joins the basal joint, with a single long and 

 slender spine at the inner distal corner. There is also a small spine 

 on the ventral surface of the basal joint just above the endopod. 



The third legs stand out at right angles to the ventral surface, 

 with their tips considerably enlarged, as shown in figure 29. 



Each fourth leg is divided to its base ; the rami are slender, taper 

 to a blunt point, and project practically their entire length behind the 

 dorsal plate. The egg strings are considerably thicker than the rami 

 of the fourth legs, and about as long as the body and legs together. 



Color (preserved material), a uniform yellowish brown. 



Total length of bodj^, 2.50 mm. ; of cephalothorax, 0.75 mm. Width 

 of cephalothorax, 0.65 mm. ; of anterior body, 1.15 mm. ; of posterior 

 body, 1 mm. Length of fourth legs, 1.85 mm. ; of egg strings, 3-85 mm. 



/Specific characters of male. — Cephalothorax exceptionally large, 

 wider than the body and about half the entire length, the posterior 

 margin widened and bilobed, the anterior margin narrowed and 

 squarely truncated. Body narrowed where it joins the cephalo- 

 thorax, widened through the bases of the first and second legs and 

 in the genital segment. 



First antennae more distinctly seven-jointed than in the female; 

 second antennae and maxillipeds relatively larger and stouter. First 

 and second swimming legs like those of the female ; third legs reduced 

 to minute uni ramose stumps, easily overlooked. Fourth legs unira- 



