Marsh — JS/orth American Species of Diaptomus . 453 
second segment of the exopodite. It is spatulate in form, 
armed at the tip with blunt spines, and with very minute spines 
over its whole surface. 
Length of the female, according to Schacht, 1.37 mm. 
Length of male, 1.68 mm. According to Brewer, the female 
varies from 2.25 mm. to 2.5 mm. I have not at hand enough 
mature specimens to get a good average of size. 
Found, according to Schacht, in West Okoboji lake, Iowa. 
Brewer’s material was found near Lincoln, Nebraska. Found 
by Beardsley in Greeley, Colorado. 
The above description was written from material sent by 
Brewer. Schacht’s description does not correspond in all de¬ 
tails. Lie states that the female abdomen is asymmetrical. 
This asymmetry was not noticeable in my material. He speaks 
of the peculiar hook of the male fifth foot as on the first seg¬ 
ment of the exopodite. In my specimens it is on the second 
basal segment, and his figures show the same situation. This 
lack of correspondence between Schacht’s figure and descrip¬ 
tion has already been noted by Beardsley (’02). On the second 
segment of the exopodite of the female fifth foot, Schacht says 
there are two spines, of which the outer is the longer. I find 
three spines, and the innermost is the longest. His figure 
makes the inner the longest. Llis figure, too, omits the terminal 
spines of the endopodite of the female fifth foot, although he 
speaks of them in his text. There is a difference, too, in the 
length of the abdominal segments as compared with the Ne¬ 
braska material. 
If these differences exist and are constant, D. nebraskensis 
must be considered a variety of D. clavipes. I think it prob¬ 
able, however, that if material were available for a compari¬ 
son of specimens from the two localities, it would appear that 
there is not even a varietal difference. 
