Marsh — North American Species of Diaptomus. 443 



In the description as given above, I have adhered very close- 

 ly to the description given in De Gueme and Richard's Re- 

 vision, and the changes which I have made have been mostly 

 in the way of minor additions. It would appear that the 

 specimens of the three localities thus far known are very nearly 

 identical in their structure. 



DIAPTOMUS LEPTOPUS Forbcs. 



Plate XX, figs. 1, 2, 5, 7. 



1882, D. leptopus Forbes, p. 646 ; pi. VIII, figs. lY-19. 



1884. D. longicornis var. leptopus Herrick, p. 140. 



1889. D. leptopus DeGuerne and Richard, p. 21; pi. II, fig. 



19 ; pi. Ill, fig. 9. 

 1893. D. leptopus Marsh, p. 195; pi III, figs. 4, 5. 

 1895. D. leptopus Herrick and Turner, p. 64; pi. II, figs. 



l-10;pl. IX, fig. 9. 

 1897. D. leptopus Schacht, p. 130. 



The last cephalothoracic segment is armed laterally with 

 two minute spines. 



The first abdominal segment of the female is somewhat less 

 in length than the remainder of the abdomen and the furca. 

 It is dilated on the sides, and armed laterally with minute 

 spines. The second segment is very short, and hardly dis- 

 tinguished from the first. The third segment and the furca 

 are very nearly equal in length. The inner margins of the 

 furca are ciliate. 



The antennae reach to the end of the furca. The right male 

 antenna is much swollen anterior to the geniculating joint; 

 the antepenultimate segment is armed with a hyaline lamella 

 extending its whole length, and prolonged slightly beyond the 

 distal end of the segment. 



The first basal segment of the female fifth foot is armed with 

 the customary spine. The second basal segment has the minute 

 lateral hair at about the middle of its outer margin. The ex- 

 opodite is composed of two segments. The third segment is 

 represented by two spines, the outer being the smaller. The 



