North American Species of Diaptomus. 127 



'distinct and broader basal portion than the individuals from 

 Yellowstone Park. Both the inner and outer margins of the 

 second segment of the outer ramus are hairy in Dr. Forbes's 

 specimens, but much more pronouncedly so in the specimens 

 from Portage Slough. 



The fifth pair of feet of the male are very similar to the 

 corresponding appendages of I), clavipes sp. nov. and D. 

 leptopus Forbes. Dr. Forbes notes the differences between his 

 species (piscina and leptopus), and from clavipes both may be 

 distinguished at a glance by the inner rami and the other 

 peculiarities mentioned in the description of that species. A 

 characteristic of D. piscina, and one which was neither figured 

 nor described, is a fin-shaped process on the middle of the 

 anterior surface of the second basal segment of the right fifth 

 foot of the male. This is armed on the inner margin with a 

 row of bead-like tubercles and is more distinct in the Portage 

 Slough specimens. This process corresponds to a similar 

 one in D. clavipes. The lower two thirds of the inner margin 

 of this segment are hairy, and at the end of the proximal 

 third is a small triangular projection. 



The terminal hook and the marginal spine of the outer ramus 

 of the right male foot are both denticulate on the lower half of 

 the inner margin. 



In the "Preliminary Pieport on the Aquatic Invertebrate 

 Fauna of the Yellowstone National Park, Wyoming, and of, 

 the Flathead Region of Montana" the inner ramus of the right 

 fifth leg of the male (Fig. 22) by mistake was not figured. 

 The description was correct but the figure did not correspond. 



The first and second segments of the outer ramus of the left 

 fifth foot of the male are hairy on the inner margin. 



The length of the Portage Slough specimens is as follows : 

 female, 2.11 mm; male, 2.06 mm. 



Diaptomus lintoni Forbes. (PI. XXVII. , Fig. 1.) 



Diaptomus lintoni, Forbes, '93, p. 252, PI. XLIL, Fig. 26-28. 

 Diaptomus lintoni, Herrick and Turner. *95, p. (58, PI. V., Fig. 12. 



"A large red species occurring commonly with D. shoshone, 

 but distinguishable from it at a glance by its different shape, 



