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. YI, 
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 furcal rami are about equal. 
The furcal rami are ciliate. The setae are very long and slen¬ 
der; the internal seta is much more nearly equal to the others 
than is generally the case. 
The antennae are 2 5-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 
