462 Wisconsin Academy of Sciences, Arts, and Letters. 
Length of female, 1.132 mm. Length of male, 1.115 mm. 
This species was found in material collected by Professor 
H. B. Ward in Dead lake, Lake Michigan, Lake Bocks, and 
Mirror lake,—all these lakes being in the vicinity of Pike’s 
Peak. It was especially abundant in the collections from 
Lake Michigan. 
DIAPTOMUS WASHINGTONENSIS Sp. n 07 . 
Plate XXII, figs. 5, 8, 9. Plate XXIII, fig. 2. 
One of the smaller species. The first cephalothoracic seg¬ 
ment is somewhat longer than the combined length of the three 
following segments. The last cephalothoracic segment is 
armed with minute lateral spines. The first segment of the 
female abdomen is as long as the rest of the abdomen. It is 
expanded laterally and in front and bears two small spines 
laterally. On the posterior end on the right side it bears a 
finger-like process projecting backward. The second segment 
is ordinarily about one-half the length of the third. The fureal 
rami are about twice as long as their width and are setose on 
the inner margin. 
The antennae are 25-segmented, slightly longer than the en¬ 
tire body. The right male antenna is much swollen anterior 
to the geniculating joint, and the antepenultimate segment 
bears a recurved hook which is continuous with a lateral la¬ 
mella extending back one-half the length of the segment. 
The first basal segments of the female fifth feet are armed 
with rather large spines. The lateral hairs of the second basal 
segments are very long and slender. The exopodite is composed 
of two segments, the third segment being represented by two 
small spines. In addition to these spines, there are sometimes 
present two other very minute spines. The second segment is 
prolonged into the customary hook, which is denticulate on the 
inner margin. The endopodite is slightly longer than the 
first segment of the exopodite, is composed of one segment, and 
armed on the inner margin of the tip with hairs, and has two 
rather long terminal spines. 
