396 Wisconsin Academy of Sciences, Arts, and Letters . 
this form. The relationship of this group, then, may be ex¬ 
pressed by the following diagram: 
sicilis 
minutus 
D. Tyrelli has no appendage of the antepenultimate segment 
of the right male antenna, but the structure of the male fifth 
foot leads me to think that it should be classed with this group. 
It must be considered as somewhat distinctly separated from 
the rest of the group, and its phylogeny is uncertain. 
THE LEPTOPUS GROUP. 
This includes D. leptopus, leptopus var. piscinae, conipe - 
daius, stagnalis, Lintoni, spatulocrenatus and clavipes .. . D, 
conipedatus, D. spatulocrenatus and D. stagnalis have a hook 
on the antepenultimate segment of the right antenna of the 
male. The others have a lateral hyaline lamella. D. lepto¬ 
pus, D. leptopus var. piscinae, D. conipedatus and D. clavipes 
have a hook in the posterior face of the second basal segment 
of the right fifth foot of the male, this hook being most pro¬ 
nounced in the case of D. clavipes. The published figures do 
not indicate the presence of such a hook in D. Lintoni or D. 
stagnalis, but Schacht’s description of D. stagnalis speaks of 
the presence of a “large, smooth, hyaline lamella.” This may 
represent the hook of the other species. In the female fifth 
foot, the second segment of the exopodite has either two or 
three spines in D. leptopus, and three in D. clavipes, D. conipe¬ 
datus, D. spatulocrenatus and D. Lintoni. In D. stagnalis the 
exopodite is distinctly three-segmented. The endopodites of 
the female fifth feet in D. stagnalis are two-segmented. 
