62 Illinois State Laboratory of Natural History. 



sacs as far back in the abdomen as the anterior border of 

 the third segment. 



The female varies in length from .9 mm. to 1.26 mm., and 

 the male is usually about .2 mm. shorter. The largest 

 specimens measured came from Portage La Prairie, Manitoba. 



This is a beautifully colored species. The ground color is 

 reddish brown. The second cephalothoracic segment, the 

 last abdominal segment with the stylets, the swimming feet, 

 and the last segment of the first antennae are sky-blue. A 

 yellow spot surrounds the eye. 



The egg-sacs are dark blue or black. 



The best character for the ready recognition of this species 

 is its strong superficial resemblance to the genus Cantho- 

 camptus. 



GENERAL DISTRIBUTION OF CYCLOPS IN NORTH AMERICA. 



Of the eighteen species and three varieties of Cyclops which 

 have been reported as occurring in North America, but three 

 species and two varieties, namely, ater, modestus, and edax, 

 and varieties insectus and brevispinosus of viridis are char- 

 acteristic of America, while the remaining fifteen species and 

 one variety are common to both Europe and America. 



Probably bicuspidatus, serrulatus, viridis, albidus, and edax 

 might be found in any state in the Union, so general is their 

 distribution. 



In the Great Lakes by far the most abundant species are 

 bicuspidatus and edax. Often either one or the other of these 

 two species will constitute nearly the whole of the crustacean 

 plankton. 



Collections from the high lakes and ponds of the Northwest 

 usually contain Cyclops, often in considerable numbers, but 

 they are never present in such great quantities as is the genus 

 Diaptomus and the Cladocera. The commonest of these 

 mountain forms are as follows: bicuspidatus, viridis var. 

 insectus, serrulatus, and albidus, though viridis var. brevis- 

 pinosus, bicolor, dybowskii, modestus, and edax have been 

 found in such situations. In collections from Crater Lake, 

 Oregon, I found a very few specimens of albidus and ser- 



