114 Illinois State Laboratory of Natural History. 



produced. Inner ramus of right leg not reaching end 

 of first segment of outer ramus ; apex bluntly rounded. 

 Left leg reaching about to end of first segment of outer 

 ramus of right leg ; inner ramus reaching middle of last 

 segment of outer ramus, margins sinuously curved. 



siciloides. 

 43 (42). Process stout, reaching to middle of penultimate 

 article or beyond. Marginal spine below middle of seg- 

 ment, less than half as long as segment. Terminal hook 

 not much if any longer than the two preceding seg- 

 ments. First segment of outer ramus with hyaline 

 lamina on inner margin, which is much produced at 

 the outer apical angle. Inner ramus of right leg conical, 

 not reaching end of first segment of outer ramus. Left 

 leg reaching to tip of first segment of outer ramus of 

 right leg. Inner ramus extending beyond middle of 

 last segment of outer ramus ; margins parallel ; armed 

 on outer margin near base with small hemispherical 

 process. signicauda. 



KEY TO THE NORTH AMERICAN SPECIES OF DiaptomilS, BASED ON 

 THE CHARACTERISTICS OF THE FEMALE. 



1 (18). Inner ramus of fifth pair of legs noticeably shorter 



than first segment of outer ramus. 



2 (10). Outer ramus distinctly or indistinctly 3-segmentrd. 



3 (4,7). Inner ramus distinctly 2-segmented, the first seg- 



ment very short and subquadrate ; barely reaching end 

 of first segment of outer ramus ; armed with two straight 

 hairy spines, almost as long as the ramus. Second 

 segment of outer ramus with small spine near base of 

 third segment ; spinose on both margins. Third seg- 

 ment armed with two stout spines, the inner hairy, 

 about twice as long as the outer, which is about as 

 long as the spine on the preceding segment. Last 

 thoracic segment strongly produced. First abdominal 

 segment longer than remainder of abdomen, greatly 

 dilated, armed on each side with large spine ; second 

 segment shorter than third. Furcal rami about as 



