460 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.49. 



basal segment is of moderate length. The first segment of the 

 exopodite is more than twice as long as wide. The hook is only 

 slightly curved and is finely denticulate on both inner and outer 

 margins. It is armed with three spines, the innermost being the 

 longest. The inner two spines represent the third segment. The 

 endopodite is long and slender, 1-segmented, and exceeds in length 

 the first segment of the exopodite. It is setose at tip, and armed with 

 two long terminal spines which are inserted well back from the end of 

 the endopodite. In the male fifth feet the spines of the first basal 

 segments are rather prominent and acute. The second basal segment 

 of the right foot is twice as long as broad. The lateral hair is situated 

 about at the beginning of the distal third. The first segment of the 

 exopodite is quadrate and bears on the inner distal angle a hyaline 

 process which varies somewhat in size and form; it most commonly 

 has a rounded extremity but may be nearly triangular in form. The 

 second segment is strongly curved and equals in length the first basal 

 segment. The lateral spine is straight or slightly curved, is rather 

 small, and is situated just distad of the middle. The terminal hook 

 is slender, slightly curved, and equal in length to the rest of the foot 

 with the exception of the first basal segment. It is denticulate on 

 the inner margin. The endopodite is small, variable in length, but 

 not as long as the first segment of the exopodite. It is ordinarily 

 pointed at the distal extremity, but in some individuals it is rounded. 

 The left foot reaches to the end of the first segment of the right 

 exopodite. The second basal segment is as long as wide, and strongly 

 convex on the inner margin. The lateral hair is situated near the 

 distal end. The first segment of the exopodite is longer than wide. 

 The second segment is about one-half the length of the fu"st, and the 

 inner surface is a convex setose pad. The segment is terminated with 

 two digitiform processes, of which the outer is the longer. The 

 endopodite is long and slender, reaching to the middle of the second 

 segment of the exopodite. It is either 1-segmented or indistinctly 

 2-segmented. The tip is distinctly setose. 



Length according to Poppe: Female, 1 mm.; male, 1.5 mm. 



Length according to Lilljeborg: Female, 1.9 mm.; male, 1.8 mm. 



Specimens from Alturas Lake averaged: Female, 1.258 mm.; male, 

 1.15 mm. 



It seems probable that in Poppe's description the lengths for the 

 female and male were transposed. 



The original description by Poppe was from material collected at 

 Summit Lake in the Canadian Rockies, at a heighth of 5,300 feet. 

 Lilljeborg's material was from Centerville, Cahfornia. It has also 

 been found in collections made by the United States Fish Commission 

 in Alturas Lake, Idaho, and in the Pribiloff Islands, Alaska, and by 

 the author in Yellowstone Park and in Lake Tahoe. 



