Marsh — North American Species of Diaptomus. 457 



The spines of the first basal segments of tlie fifth feet of the 

 male are rather long and slender. The second basal segment 

 of tlie right foot is about twice as long as broad, and convex on 

 inner and outer margins. The lateral hair is situated at about 

 two-thirds of its length. It bears a small tubercle on the pos- 

 terior surface, near the inner margin, at about one-thirJ. its 

 length. The first segment of the right exopodite is twice as 

 long as wide, convex on the outer margin and concave on the 

 inner; the second segment is three times as long as wide, 

 strongly concave on the inner margin and convex on the outer. 

 The lateral spine is near the outer distal angle, is of medimn 

 length and slightly curved. The terminal hook is stout, nearly 

 as long as the segment, bent sharply at about the middle. It is 

 denticulate on the inner margin. The endopodite is rudimen- 

 tary, being represented by a short, curved process. 



The left foot, in length, does not reach the end of the first 

 segment of the exopodite of the right foot. The second basal 

 segment of the left foot is trapezoidal in form, three-fourths as 

 long as the corresponding" segment of the right foot. The lat- 

 eral hair is at about two-thirds its length. The first segment 

 of the exopodite is one-half as wide as the second basal seg- 

 ment, is twice as long as wide, with rounded apical angles ; the 

 inner distal angle is setose. The second segment is less than 

 two-thirds the leng-th of the first, is concave on the inner mar- 

 gin and convex on the outer. It is armed at the tip with a 

 stout finger-like process at the outer angle, and a slender curved 

 process at the inner angle. The process at the outer angle is 

 finely denticulate on the inner margin, and the process at the 

 inner angle is setose. The inner margin of the second segment is 

 setose. The endopodite is two-segmented and nearly equals in 

 length the exopodite. The first segment is slender. The sec- 

 ond segment is oval, crenate on the inner margin, and setose at 

 the tip and on the inner and anterior surfaces. 



Length of female, 1,47-1.58 mm. Length of male, 1.30- 

 1.33 mm. 



This was found in Wig'wam pond, I^antucket. 



Pearse's paper containing the description, of which the above 

 is nearly a verbatim copy, modified only to correspond to the 



