Lehmann—Variations in Form and Size of Cyclops. 283 
swimming feet of C. americanus as of chief importance for spe¬ 
cific distinction. Forbes, ? 97, regards the features under con¬ 
sideration as often of doubtful value even for varietal distinc¬ 
tion. He says: “So variable is C. insectus, [(7. americanus 
Marsh], found as it is in an endless variety of situations and 
localities, that the lack of a single spine on the distal segment 
of the outer ramus of the first and fourth feet is not sufficient 
ground for the distinction of even a variety, for I find, as does 
Dr. Schmeil, that the armature of the swimming feet is not in 
all species absolutely constant.” It may be noted here', how¬ 
ever, that a constant armature of the swimming feet is not of 
necessity more valuable for specific distinction than a variable 
one, if only definite limits of variation can be established for 
the armature in question. Marsh has distinguished between 
C. brevispinosus and C. ameHcanus by a supposed constantly 
different armature of the fourth swimming feet in either 
•species. 
The specimens from which the accompanying measurements 
and plates were obtained, were taken entirely from the collect 
tions of Professor Marsh. The prepared slides in his posses¬ 
sion were considered, and a fairly large number of specimens 
were selected from his bottled collections. 
Only egg-bearing females of either species were considered, 
these giving the typical form of the fully developed individual. 
All the specimens of C. brevispinosus came from comparatively 
large bodies of water, of varying depths, but in no sense pools. 
They came also entirely from the region of the' Great Lakes, 
thus perhaps not representing the whole species. The C. amer¬ 
icanus examined came with but few exceptions', from pools, 
usually small and weedy, and varying greatly in depth and 
character with the changes' in temperature and the seasons. 
They were obtained from widely different parts of the United 
States, and thus give a more general idea of the extent of varia¬ 
tion. 
The specimens of C. americanus represent a wider area than 
those of C. brevispinosus, but, on the other hand, are fewer in 
number. 
