A3T. 5. NORTH AMERICAN PARASITIC COPEPODS WILSON. 61 



External specific characters of female. — Body elongate and quite 

 thick-set, made up of a distinct cephalothorax, four free thorax seg- 

 ments, a genital segment, and three abdomen segments. Carapace 

 elliptical, a little longer than wide, about one-fourth of the entire 

 length, with an evenly curved outline. Its width in proportion to 

 that of the second segment is as 6 to 7. Both pairs of antennae 

 usually project from the anterior margin, while from the sides a pair 

 of huge maxillipeds stretch back to the center of the second segment. 



First three free segments about the same size, their length less 

 than half their width. Each is entirely covered dorsally with a 

 plate whose ends curve around the sides of the segment and reach 

 a short distance onto the ventral surface. Each plate overlaps the 

 one behind it like shingles on a roof, while the ends of all of them 

 are free and stand out a littia from the ventral surface. There is 

 space enough between these ends for the thoracic legs to work freely. 

 The posterior corners of the fourth segment are prolonged into short 

 semicircular lobes, which project from beneath the posterior edge 

 of the dorsal plate. The fifth segment is much narrower than the 

 other three, obovate in shape, and considerably narrowed where it 

 joins the fourth segment. The dorsal plate is the same shape as 

 the segment, with a three-lobed posterior margin, the middle lobe 

 being much wider than the lateral ones and overlapping the genital 

 segment. This plate does not curve around the sides of the seg- 

 ment and hence is invisible from the ventral surface. 



The genital segment is transversely elliptical, narrower than the 

 fifth segment, with strongly convex sides. Posteriorly it is slightly 

 emarginate, and this, with the overlapping median lobe of the fifth 

 segment, gives it something of a dumb-bell shape in dorsal view. 



The abdomen is about half the width of the genital segment and 

 three-jointed, the first two joints very short, the terminal one much 

 longer and hemispherical. The anal laminae are narrow, spindle- 

 shaped, and longer than the last abdomen segment, with three short 

 terminal setae, and a fourth still shorter one on the outer margin. 

 Egg strings a little wider than the abdomen and not quite as long 

 as the entire body, with 25 or 30 eggs in each string. 



The first antennae have 10 or more joints, the divisions at the 

 base being very indistinct. The second, the fourth, and the two 

 terminal joints are longer than the others, which are all about equal. 

 Every joint bears at least one seta on its anterior margin, the second 

 joint has two with four others on its ventral surface, and the fourth 

 joint also has two, with another one on its ventral surface. The 

 last two joints are ellipsoidal, the terminal one tipped with five or 

 six long setae. 



The second antennae are four- jointed, the first and third joints 

 about equal and considerably longer than the other two. The 

 3136— 22— Pioc.N.M.Vol.60 12 



