COPEPODA 



759 



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



foot digitiform, hyaline appendage on internal distal angle 

 of first segment of right exopodite 20 



20 (21) Lateral spine of second segment of right exopodite nearly straight, 



no blunt spine on posterior surface of this segment. 



Diaptomus tyrelli Poppe 1888. 



Widely spread in the mountain lakes of the West. 

 Length of female, 1.2 mm. 

 Length of male, 1.15 mm. 



Fig. 1181. Fifth feet of male Diaptomus tyrelli. X 190. 

 (Original.) 



21 (20) A second hyaline appendage on dorsal side of distal margin of first 



segment of right exopodite, lateral spine of second segment 

 of right exopodite strongly curved, and a blunt spine on 

 posterior surface of this segment. 



Diaptomus coloradensis Marsh 1911. 



In the Rocky Mountains in Colorado D. tyrelli is replaced by this closely 

 allied species which is, apparently, the characteristic species of the moun- 

 tain lakes of Colorado. 



Length of female, 1.38 mm. 



Length of male, 1.32 mm. 



Fig. 11S2. "FiiXhifxtoiixidXa DiaptDltms coloradensis. X 120. (Original.) 



22 (9) Antepenultimate segment of male right antenna with lateral lamella 



or terminal process 23 



23 (a6, 42) Antepenultimate segment of right antenna of male with hyaline 



lamella 24 



