Marsh—North American Species of Cyclops. 1085 
long series of measurements, but such “that one well acquainted 
with these species can distinguish them at a glance.” 
In regard to these points of difference, I can only say that 
none of them seem to me of more than varietal value. In 
regard to the indentations in the hyaline membrane of the 
last antennal segment, I find both forms in the same collection 
with every reason to think that they grade the one into the 
other. I have found, in my collections, the form with a 
single indentation the more abundant. 
Burckhardt (Burckhardt 1900, p. 640) recognizing this 
possibility of variation, states that in his specimens, the outer 
three-fourths of the membrane was uniformly indented. 
I have already discussed the variations in the crenulations 
of the second segment of the outer maxillipede. There is great 
variation in this characteristic. 
The other points of difference are minor things, differences 
which one would expect within species limits. The sixth 
point of difference, of course, can hardly be taken seriously, for 
differences which can not be accurately defined should not be 
used in the diagnosis of a species. Without doubt, if we are 
to recognize the differences on which E. B. Forbes distin¬ 
guishes edax we should have to use the name of LeeuwenhoeJcii 
Hoek, which has prior standing. 
The figures in Brady’s plate (Brady ’91) make it evident 
that Scourfeldi is the same as Leuclcarti. 
It seems probable that pulchellus of Miss Byrnes (Byrnes 
1909) is Leuclcarti. 
Cyclops Tenuis sp. nov. 
Plate LXXV, figs. 4-9; Plate LXXIX, fig. 5. 
A long slender species. The cephalothorax is oval, its 
length being more than twice its breadth; it is twice as long 
as the abdomen exclusive of the furcal rami. The segments 
of the cephalothorax do not project at their posterior angles. 
The anterior end of the first abdominal segment (PL LXXY, 
fig. 5) is somewhat larger than the posterior end; this segment 
is less in length than the three following. 
7—S. & A.—3 
