758 FRESH-WATER BIOLOGY 



15 (12) Left fifth foot of male, reaching end of first segment of right exopo- 



dite, or only slightly exceeding it 16 



16 (17) Antepenultimate segment of right antenna of male produced at 



distal end into a blunt point, first segment of right exopo- 

 dite of fifth foot with marked quadrangular hyaline appen- 

 dage Diaptomus birgei Marsh 1894. 



FlG. 1179. Diaptomus birgei, male. A , terminal segment of right antenna. X 191. 

 B, fifth feet. X 109. (Original.) 



Common in Indiana and has been found in Wisconsin and on Long Island. 

 Length of female, 1.3 mm. Length of male, 1.2 mm. 



17 (16) Antepenultimate segment of right antenna of male not produced 



into blunt point on distal end 18 



18 (19) Inner process of the terminal segment of exopodite of left male 



fifth foot falciform, no hyaline appendage of first segment of 

 right exopodite Diaptomus pallidus Herrick 1879. 



Occurs in Mississippi Valley, as far west as the foothills of the Rocky 

 Mountains, but is comparatively rare north of Iowa and Illinois. 

 Length of female, 1.2 mm. 

 Length of male, 1.04 mm. 



FIG. 1 1 80. Fifth feet of male Diaptomus pallidus. X 190. (Original.) 



