460 Wisconsin Academy of Sciences, Arts, and Letters. 



like processes. The endopodite is long and slender, reaching 

 well towards the end of the second segment of the exopodite. 

 It is setose on the inner margin of the tip. 



Length of female, 1.5 mm. Length of male, 1.3 mm. 



The original description was written from material obtained 

 in the Sierra ISTevada in California. It is probably pretty 

 widely distributed through the mountain region of the West. 

 I have found it in collections from Marlette lake, Nevada, ob- 

 tained by Professor C. F. Baker, from Boulder lake, Colorado, 

 and Hosketts lake, California, collected by Professor Chauncey 

 Juday, and from several lakes in the Lake Tahoe region col- 

 lected by Professor II. B. Ward. One peculiarity not given 

 in the diagnosis should be noted, namely that the lateral spine 

 of the exopodite of the male fifth foot does not lie in the same 

 plane with the segment, but is curved to one side. 



The projection on the first abdominal segment of the female, 

 from which the species is named, is not present in the immature 

 specimens, appearing only at maturity. 



DiAPTOMUs NUDUS Marsh. 



Plate XXI, fig. 9. Plate XXII, figs. 1, 2. 



1904. Diaptomus nudus Marsh, p. 147 ; pi. XXX, figs. 1, 2^ 

 4, 5. 



Of moderate size. The first cephalothoracic segment is 

 nearly equal in length to the rest of the cephalothorax. The 

 last cephalothoracic segment is armed laterally with two mi- 

 nute spines. 



The first abdominal segment of the female is somewhat long- 

 er than the rest of the abdomen. It is dilated laterally and 

 armed on each side with a sharp spine. These spines are at 

 about the termination of the first third of the segment. The 

 distal margin of the segment is extended on the right side in 

 a conical process which extends beyond the second segment. 

 The second segment is very short, and is nearly covered by 

 the first. The third segment is about one-third the length of 

 the first, and is somewhat shorter than the furca. 



