404 Wisconsin Academy of Sciences, Arts , and Letters. 
ANALYTICAL KEY TO THE NORTH AMERICAN SPECIES OF DIAPTO- 
MUS BASED ON THE CHARACTERS OF THE MALE. 
Antepenultimate segment of the male right antenna with¬ 
out a district appendage, 
Antepenultimate segment slightly produced at the 
distal end into a blunt point, first segment of 
right exopodite with marked quadrangular hy¬ 
aline appendage, . Birgei 
Right and left feet nearly equal in length, terminal 
hook of right foot symmetrical, . oregonensis 
Left foot shorter than right, 
Left foot reaching beyond first segment of the ex- 
opiodite, 
Terminal hook of right foot uniangular, right 
endopodite equal in length to first segment 
of the exopodite, . Reighardi 
Terminal hook biangular, right endopodite large, 
longer than first segment of the exopo¬ 
dite, . mississippiensis 
Left foot reaching end of first segment of the 
exopodite, 
Inner process of the terminal segment of the 
left exopodite falciform, no hyaline append¬ 
age of first segment of right exopodite, . pallidm 
Inner process of terminal segment of left ex¬ 
opodite digitiform, a hyaline appendage on 
internal distal angle of first segment of 
right exopodite, . Tyrelli 
Antepenultimate segment of male right antenna with 
hyaline lamella, 
Hyaline lamella broad, extending beyond the end of 
the segment, second basal segment of the right 
exopodite armed on the posterior surface with a 
small hook, ... leptopus 
Hyaline lamella narrow, extending beyond the end of 
the segment slightly, if at all, first basal segment 
armed with a hook equal in length to the first 
segment of the exopodite, . clavipes 
.Antepenultimate segment of the right antenna bears 
a slender straight process, 
This process is much shorter than the penultimate 
segment, 
Right endopodite rudimentary, 
Lateral spine of the second segment of the right 
exopodite is terminal, . Lintoni 
Lateral spine of the second segment of the ex- 
