Marsh — North American Species of Diaptomus. 453 



second segment of the exopodite. It is spatnlate 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, ISTebraska. 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. He 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 

 segTiient 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. His 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. nebrashensii^ 

 must be considered a variety of D. clavipes. 1 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. 



