FRESH-WATER BIOLOGY 



24 (25) 



Hyaline lamella broad, extending beyond the end of the segment, 

 second basal segment of right exopodite of male fifth foot 

 armed on the posterior surface with small hook. 



Diaptomus leptopus Forbes 1882. 



Found generally distributed through the 

 Mississippi Valley, and extending into Canada. 

 The variety piscinae occurs in some of the 

 more northern collections and as far west as 

 Flathead Lake, Montana. This differs from 

 typical leptopus mainly in the greater length 

 of the endopodites of the male fifth feet and 

 in the fact that in the female fifth feet the 

 third segment of the exopodite is indistinctly 

 separated and armed with two spines with a 

 third one present on the second segment. 

 This third spine is absent in leptopus. 



Length of female, 1.5 to 1.89 mm. 



Length of male, 1.4 to 1.83 mm. 



FIG. 1183. Diaptomus leptopus, male. A, ter- 

 minal segments of right antenna. X 185. B. 

 fifth feet. X83- (Original.) 



Hyaline lamella narrow, extending beyond the end of the segment 

 slightly, if at all; first basal segment of right fifth foot of 

 male armed with hook equal in length to first segment of 

 exopodite. ...... Diaptomus clavipes Schacht 1897. 



Has been found in three locali- 

 ties, in West Okoboji Lake, Iowa, 

 near Lincoln, Nebraska, and at 

 Greeley, Colorado. 



Length of female from 1.37 

 to 2.5 mm. 



FIG. 1184. Diaptomus clavipes, male. 

 A, fifth feet. X 83- B, terminal 

 segments of right antenna. X 141. 

 (Original.) 



26 (23, 42) Antepenultimate segment of right antenna of male bears a slender 

 straight process 27 



