422 Wisconsin Academy of Sciences. Arts, and Letters. 



Length of female, 1.27 luni. Length of male, 1.124 mm. 



This species was found in material collected by Professor C. 

 F. Baker in Lake Lagimita, Palo Alto, California. 



This form is closely related to D. franclscanus 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. Bal-eri 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. UOV. 



Plate XVI, figs. Y, 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 some\vhat 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 arniod 

 with the customary spines. The lateral hairs of the second 

 basal segments are rather long. The exopodite is composed of 



