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 crenulationa 

 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 Leeuwenhoehii 

 Hoek, which has prior standing. 



The figures in Brady's plate (Brady '91) make it evident 

 that Scourfeldi is the same as LeucJearti. 



It seems probable that pulchellus of Miss Byrnes (Byrnes 

 1909) is Leucharti. 



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 (PI. LXXV, 

 fig. 5) is somewhat larger than the posterior end; this segment 

 is less in length than the three following. 

 7— S. & A.— 3 



