398 Wisconsin Academy of Sciences, Arts, and Letters. 
signicauda and D. Judayi have a hyaline lamella on the first 
segment of the right exopodite. D. washingtonensis alone has 
the primitive character of a two-segmented endopodite in the 
male fifth foot. D. Judayi has the most pronounced spines on 
the first segment of the female abdomen., It seems that there 
should be no question of putting these species together on the 
ground of the posterior process of the first segment of the fe¬ 
male abdomen, although this appears late in the development 
of the individual and it is very possible that the peculiarity 
originated in different lines. , 
With this group I should place D. Tryborrti, although it is 
somewhat aberrant in many details of structure. The asym¬ 
metry of the female abdomen would lead us to conjecture a re¬ 
lationship with the signicauda group, but a relationship much 
more remote than that of the other members. The male fifth 
foot, while peculiar in many respects, yet bears a marked re¬ 
semblance to the fifth feet of the group in question. In the 
“dorsal hump,” too, there is a reminder of D. signicauda. The* 
group seems to be nearly related to the tenuicaudatus group*, 
and is probably an offshoot of it. 
One species of this group can hardly be picked out as the* 
most primitive. I have called it the signicauda group, simply 
because that was the first of the species to be described. 
THE ALBUQUERQUENSIS GROUP. 
In this group are included D. albuquerquensis, dorsalis,, 
asymmetricus, purpureus and saltillinus. All have a hooked 
process on the antepenultimate segment of the right antenna of 
the male. The principal reason for putting them together, 
however, is the similarity of the male fifth feet. In all, the 
endopodites are short and composed of a single segment. In 
all, except D. albuquerquensis and D. saltillinus, there is a hya¬ 
line process on the inner margin of the second basal segment of 
the right foot; D. saltillinus has a tubercle on the inner margin, 
and both D. saltillinus and D. albuquerquensis have a peculiar 
process on the posterior surface of this segment. In all there is a 
transverse ridge on the posterior surface of the first segment of 
