Marsh—North American Specves of Diaptomus. 407’ 
tinctly two-segmented, the left one-seg- 
mented, ... washingtonensis 
The right endopodite equals or only slightly ex¬ 
ceeds the first segment of the exopodite, 
The terminal segment of the right exopodite 
has a transverse ridge on its dorsal sur¬ 
face, the lateral spine exceeds in length 
the segment, . albuquerquensis 
The terminal segment of the right exopodite 
does not have an oblique ridge on its dorsal 
surface, the lateral spine is short, about one- 
half the length of the segment, . novamexicanus 
The terminal processes of the left exopodite are 
digitiform, the right endopodite shorter than 
the first segment of the exopodite, 
The right endopodite triangular in form, first 
segment of the exopodite without hyaline 
appendage, . nudus 
The first segment of the right exopodite with 
hyaline appendage, 
Appendage at the inner distal angle, endopo¬ 
dite about equals the first segment of the 
exopodite, . signicauda 
Appendage on inner distal half, quadrangular 
in form, endopodite much shorter than the 
first segment of the exopodite, . siciloides 
The first segment of the right exopodite with 
a transverse ridge, second segment with 
oblique ridge and hyaline process near the 
outer margin, . purpureus 
ANALYTICAL KEY TO THE NORTH AMERICAN SPECIES OF DIAPTO¬ 
MUS BASED ON THE CHARACTERS OF THE FEMALE. 
The endopodites of the fifth feet are shorter than the 
first segments of the exopodites. 
The first antennae do not reach the end of the furca, 
The endopodites are one-segmented, 
The exopodites are two-segmented, the fifth 
cephalothoracic segment has a dorsal 
process, the first abdominal segment is 
asymmetrical, its distal end being ex¬ 
panded to the right, . Trybomi 
The exopodites are three-segmented, there is no 
dorsal process, the abdomen is symmetrical, . purpureus 
The fifth cephalothoracic segment has a dorsal 
process, the first abdominal segment is asym- 
