Marsh — North American Species of Diaptomus. 473 



about midway of its length, is an oblique ridge. The terminal 

 hook is longer than the rest of the foot, regularly curved and 

 finely denticulate on the inner margin. The right endopodite 

 is one-segTtiented, about equal in length to the first segment of 

 the exopodite, and is setose at the tip. 



The left foot reaches Ijeyond the end of the first segment of 

 the exopodite. The second basal segment is elongate, but 

 shorter than the corresponding segment of the right foot. The 

 lateral hair is situated at rather more than two-thirds the 

 length of the segment. The first segment of the exopodite is 

 about twice as long as wide; the inner margin is convex and 

 setose. The second segment of the exopodite is about equal in 

 length and width; it is terminated by a blunt process and a 

 slender, curved spine; its inner margin has two setose pads. 

 The endopodite is slender, one-segmented, equal in length to 

 the first segment of the exopodite, and setose at the tip. 



Length of female, 1.765 mm. Length of male, 1.581 mm. 



Localities: Albuquerque, New Mexico, City of Mexico, and 

 Hugo, Colorado. 



It was found impossible to get authoritative examples of this 

 species, as the material was not preserved by Herrick, and the 

 author was unsuccessful in dredging in the same locality. The 

 description is from the material obtained in pools near Hugo, 

 Colorado. Herrick does not mention or figure the tooth on the 

 inner margin of the first basal segment of the right fifth foot of 

 the male, or the dorsal tooth on the cephalothorax of the female. 

 While it is possible that these features, which were not de- 

 scribed either by Pearse, are local variations, it does not seem 

 probable, inasmuch as the correspondence is so complete as far 

 as the published descriptions go. It seems probable that these 

 features were overlooked. 



It may be noticed that D. aXbiiquerquensis, D. dorsali^ and 

 D. saltillinus are very closely related to each other, and it is 

 possible that intermediate forms may be found. 



Schacht describes D. albuquerquensis from material collected 

 in Florida. Just wliat Schacht had it is pretty difiicult to tell, 

 a« he gives onlv two figures, but it seems evident that D. alhu- 



