Marsh—North American Species of Diaptomus. 397 
D. Lintoni has been found only in the Yellowstone park. D. 
conipedatus has thus far been found only in Louisiana, and 
D. clavipes in Iowa and Nebraska. D. spatulocrenatus has 
been found only in the island of Nantucket. D. stagnalis prob¬ 
ably occurs generally throughout the Mississippi valley, and D. 
leptopus not only in the Mississippi valley but north into Brit¬ 
ish America. , , 
I have called this the leptopus group because D. leptopus is 
the most common species. In many respects, however, D. stag¬ 
nalis may be considered the more primitive. This is notably 
the case in the characters of the female fifth feet—the threc- 
segmented exopodite, and the two-segmented endopodite. From 
its distribution, one would think of D. leptopus as the more an¬ 
cient form. In the antennal armature, D. stagnalis, D. coni¬ 
pedatus, D. spatulocrenatus and D. Lintoni are most nearly 
alike. 
I think one can do little more than guess at the relationships 
of the members of the group. D. clavipes is apparently the 
most specialized. The probable relationships may be put, pro¬ 
visionally, as follows: 
clavipes 
leptopus 
stagnalis 
THE SIGNICAUDA GROUP. 
This consists of D. signicauda, washingtonensis, nudus and 
Judayi. They are put together because of the common character 
of the posterior process on the female abdomen. D. J udayi has 
a straight process on the antepenultimate segment of the right 
antenna of the male. The others agree in having a hook. D . 
