398 Wisconsin Academy of Sciences, AHs, and Letters. 



signicauda and D. Judayi have a hyaline lamella on the first 

 segment of the right exopodite. D. wasJiingtonen-sis 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 seemsi 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. Tryhordi, a^lthough it is 

 somev^hat 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 AI.BUQUERQTTENSIS GltOUP. 



In this group are included D. albuqaerquensis, 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. Oilhuqusrquensis 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. alhuquerquensis 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 



