Marsh — North American Species of Diaptomus. 429 



DIAPTOMUS ASHLANDI Marsh. 



Plate XVII, figs. 6, 8, 10. 



1893. Diaptomus Ashlandi Marsh, p. 198 ; pi. Ill, figs. 11-13. 

 1895. Diaptomus Ashlandi Herrick and Turner, p. 60 ; pi. VI, 



figs. 4-6. 

 1895. Diaptomus Ashlandi Marsh, p. 7 ; pi. VII, fig. 2. 

 1897. Diaptomus Ashlandi Schacht, p. 166 ; pi. XXXII, figs. 



1-4. 



A small, slender species. The suture of the first cephalotho- 

 racic segment is very marked. The first segment equals the 

 three following in length. The last segment is armed with 

 minute lateral spines. 



The first segment of the female abdomen equals in length the 

 rest of the abdomen. It is somewhat dilated laterally and bears 

 two minute lateral spines. The second segment is shorter than 

 the third, and the third and the f ureal rami are about equal. 

 The furcal rami are ciliate. The setae are very long and sleu- 

 der; the internal seta is much more nearly equal to the others 

 than is generally the case. 



The antennae are 25-segmented and reach beyond the end of 

 the furca. The right male antenna is swollen anterior to the 

 geniculating joint, and bears on the antepenultimate segment a 

 slender appendage, slightly enlarged at the tip, which slightly 

 exceeds in length the penultimate segment. The form of this 

 appendage varies somewhat, the enlarged tip not being always 

 evident. 



The spines of the first basal segments of the female fifth feet 

 are very small. The lateral hair of the second basal segment is 

 very long, equaling the length of the first segment of the exopo- 

 dite. The first segment of the exopodite is twice as long as 

 wide. The hook of the second segment is long and slender and 

 slightly curved. It is finely denticulate on the inner margin. 

 The whole second segment slightly exceeds in length the first 



