Marsh — North American Species of Diaptomus. 417 



of the right foot is twice as long as broad, and the rather long 

 lateral hair is situated at about two-thirds of its length. The 

 first segment of the exopodite is longer than broad. The sec- 

 ond segment is twice as long as the first, and bears upon its 

 inner margin at the end of the proximal third a small spine. 

 The outer distal angle of the segment is truncated, and the 

 latoral spine, which is slender and slightly curved, is situated 

 at the beginning of this truncation. The terminal spine is 

 slender, curved, and slightly angular, and about once and a 

 half the length of the first segment of the exopodite. It is 

 denticulate on the inner margin. The right endopodite is slen- 

 der, of one segment, pointed at the tip, with minute terminal 

 setae, and equal in leng-th to the first segment of the exopodite. 



The left male fifth foot reaches about one-third the length 

 of the second segment of the right exopodite, although its 

 length is somewhat variable. The second basal segment is 

 quadrate and longer than broad. The lateral hair is situated 

 at about three-fourths of its length. The first segment of the 

 exopodite equals in length the corresponding segment of the 

 right foot; the distal end is about one-half the width of the 

 proximal. The second segment is one-half as long as the first. 

 It is arm.ed with an outer finger-shaped process which has a 

 small pad on its inner margin, arA an inner slender falciform 

 process which curves over the tip of the segment. This falci- 

 form process is armed with a blunt spine on its inner margin. 

 I fail to verify the armature as described by Herrick ('95, p. 

 73.) The endopodite is slender, pointed, with minute ter- 

 minal setae, and is equal in length to the first segment of the 

 exopodite. 



Length of female, 1.18 mm. Length of male, 1.043 mm. 

 These lengths are averages from specimens from St. Louis. 

 They are larger than I had obtained from Wisconsin speci- 

 mens, but not as large as the figures given by Herrick. 



Herrick's original description was of specimens found in 

 Minnesota. He afterwards reported a species "like pallidus"' 

 in Alabama. (Herrick, '87, p. 11.) In his final report he 



27— S. & A. 



