1070 Wisconsin Academy of Sciences, Arts, and Letters. 
KEY TO SPECIES OF CYCLOPS FOUND IN NORTH AMERICA. 
Antennae composed of 17 segments 
Fifth foot composed of one segment, armed with one spine and 
two long setae,—a large species of dark color, ater 
Fifth foot composed of two segments, 
Second segment of fifth foot armed with seta and short 
spine viridis 
Second segment of fifth foot armed with two setae, 
The second segment of the fifth foot is elongate, its length 
as much as twice its width, the seta of the inner 
distal angle spine-like, less than one half the length 
of the outer seta, bicuspidatus 
The second segment of the fifth foot is shorter, length 
less than twice its width, armed with two nearly 
equal setae, 
The seventeenth antennal segment is armed with a 
serrate hyaline plate, LeucJcarti 
The seventeenth antennal segment is not armed with 
a hyaline plate, tenuis 
The second segment of the fifth foot is armed with three 
setae 
The twelfth antennal segment has a sensory club, the 
egg-sacs stand out from the abdomen, the hyaline 
plate of the seventeenth antennal segment is ser¬ 
rate, or smooth, albidus 
The twelfth antennal segment has a sensory hair, the 
egg-sacs lie close to the abdomen, the hyaline plate 
of the seventeenth antennal segment is deeply 
notched, fuscus 
Antennae composed of sixteen segments, fifth foot of three seg¬ 
ments, modestus 
Antennae composed of twelve segments, fifth foot of one segment. 
Fifth foot armed with three setae, rami of swimming feet of 
Furca of variable length, armed externally with a row of 
spines, found almost everywhere. serrulatus 
Furca short, without spinous armature, a small limnetic 
species, prasinus 
Fifth foot armed with one seta, rami of swimming feet of 
two segments, varicans 
Antennae composed of eleven segments, 
Rami of swimming feet composed of three segments, phaleratus 
Rami of swimming feet composed of two segments, bicolor 
Antennae composed of eight segments, Jimbriatus 
Antennae composed of six segments, aeguoreu* 
