204 Marsh—Cyclopidce and Calanidce of Wisconsin. 
neither gives figures of the swimming feet. From the original 
description by Fischer our species differs markedly. Accord¬ 
ing to his figure the antennae reach to the third cephalothoracic 
segment, while in americcmus they hardly exceed the first. 
He makes the furca about equal in length to the last abdominal 
segment; in americanus it equals or exceeds the last two seg¬ 
ments. He gives a figure of “a foot, ” not designating which, 
but it corresponds to no one of the four in our species. 
Sars says the terminal joint of the external ramus of the 
fourth foot has two external spines; americanus has three. 
Brady’s figure of the terminal joint of the outer branch of 
the fourth foot (18, ph 20, fig. 7) corresponds to Sars’ state¬ 
ment. He also figures the terminal joint of the inner branch 
(18, pi. 20, fig. 8,) which shows a very different armature 
from that in americanus. 
Schmeil ( 41, p. 97, pi. VIII, figs. 12-14,) gives a more elab 
orate description of viridis. His formula for the spines of the 
swimming feet corresponds to the descriptions of the other 
European authors. Schmeil, however, does not consider the 
armature of the swimming feet as constant, and according to 
his view americanus should be a variety of viridis. In an exam¬ 
ination of a large number of specimens from widely separated 
localities I have found no variation in the number and arrange¬ 
ment of the spines and setae of americanus , and until such vari¬ 
ation is shown, there seems to be no alternative but to insti¬ 
tute a new species for the American form. 
C. americanus is widely distributed. It occurs quite gener¬ 
ally in stagnant pools, and is also found to some extent in 
lakes. 
Cyclops brevispinosus Herrick. 
Plate IV. Figs. 11 and 12. 
1884. C. brevispinosus Herrick (26) p. 148, pi. S, figs. 7-11. 
Cephalothorax oval, the first segment reaching about half its 
