422 Wisconsin Academy of Sciences, Arts, and Letters. 
Length of female, 1.27 mm. Length of male, 1.124 mm. 
This species was found in material collected by Professor C. 
F. Baker in Lake Lagunita, Palo Alto, California. 
This form is closely related to D. franciscanus Lillj. The gen¬ 
eral form of the male fifth feet is the same, but there are marked 
differences in the exopodite of the left foot. The projection of 
the antepenultimate segment of the right male' antenna is short¬ 
er. The endopodite of the female fifth foot is two-segmented, 
while it is composed of a single segment in D. franciscanus. 
The endopodite in D. Bakeri is armed with three terminal 
spines, while there are only two in D. franciscanus. The very 
close relationship, however, is shown in that in both species the 
exopodite is three-segmented, and both have the peculiar den- 
ticulation of the inner margin of the second segment with the 
larger teeth towards the distal end. 
DIAPTOMUS TENUICAUDATUS Sp. nOV. 
Plate XVI, figs. 7, 8. Plate XVII, figs. 2, 3. 
The first cephalothoracic segment is nearly as long as the rest 
of the cephalothorax. The last segment bears two minute 
lateral spines. 
The abdomen of the female is unusually long and slender. 
The first segment is considerably longer than the next two, and 
is somewhat enlarged in front and laterally, but has no lateral 
spines. The second segment is slightly longer than the third, 
and the furcal rami about equal in length to the second seg¬ 
ment. The length of the furcal rami is about three times their 
breadth. 
The antennae hardly reach the end of the furca. The right 
antenna of the male is swollen anterior to the geniculating joint, 
and the antepenultimate segment bears a straight process, which 
equals in length the penultimate segment. 
The first basal segments of the female fifth feet are armed 
with the customary spines. The lateral hairs of the second 
basal segments are rather long. The exopodite is composed of 
