North American Species of Diaptomus. 153 



Inner ramus of left fifth leg somewhat spatulate, extend- 

 ing slightly beyond the end of the first segment of the outer 

 ramus ; inner margin hairy ; apex bluntly rounded and hairy. 



Length of female 1.25 mm. ; of male 1.15 mm. 



The above description is based on specimens found in col- 

 lections made in Lake Calhoun, Minn., in July, 1891, and 

 differs considerably from Lilljeborg's original description in 

 de Guerne and Richard's "Revision." 



He gives the length of the female as about 1.5 mm. ; that 

 of the male, 1.4 mm. 



I did not find in a single instance that the female had the 

 last thoracic segment armed with two minute spines on each 

 side, although they were present in the male. Lilljeborg does 

 not specify to which sex this part of his description applied, 

 but I assume that he followed the usual custom of referring to 

 the female unless especially stated otherwise. 



The spines on the inner ramus of the female I found to be 

 on the inner instead of the outer margin, and they are so 

 figured by Marsh ('93). 



In most cases I found but one spine representing the third 

 segment of the outer ramus of the fifth foot of the female, 

 while one specimen was found having one outer ramus as in 

 the type, the other with only one spine. I have thought it 

 best to make the description correspond to the type in this 

 particular, regarding the variation as local since Marsh ('93) 

 figures the two spines. 



The inner ramus of the right fifth foot of the male in the 

 Minnesota specimens was longer than represented in the 

 original figures, and hairy on the inner margin and at the 

 apex. This hairiness is not mentioned in the original des- 

 cription and this ramus is figured smooth, while the inner 

 ramus of the left fifth foot, which is no more hairy than the 

 right, is hairy in the drawings. 



In the left fifth foot of the male the first segment of the 

 outer ramus, although hairy, has not the definite cushion-like 

 process figured by Lilljeborg, and the outer two digitiform 

 processes of the second segment instead of being serrate 

 within are perfectly smooth. From Herrick's statement 



