62 Illinois State iMboratorv 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 1.2G 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 Canfho- 

 cainptiis. 



GENEEAL DISTRIBUTION OF CYCLOPS IN NORTH AMERICA. 



Of the eighteen species and three varieties of Cyclops which 

 have l^een reported as occurring in North America, l)ut three 

 species and two varieties, namely, ((fcr, modcsins, and cdax, 

 and varieties iiiscctiis and hreri^piiiosKS of viridis are char- 

 acteristic of America, while the remaining fifteen species and 

 one variety are common to both Europe and America. 



Probably hicusj)hJatus, ^(')-n(l((tHS, riridts, alhuJus, 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 

 ]>icusj>id<(tus and ('d<i.r. 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 Cyeloi)s, 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 folloAvs : h'ic}ii<})'td(ttiix, r'trulU var. 

 inscctns, scrndatus, and alhidiis, though riyidis var. hycyii^- 

 phiosus, hirohry, diiJ)oicsk}i, iiiodrstii-s, and edax have been 

 found in such situations. In collections from Crater Lake, 

 Oregon, I found a very few specimens of idh'nhix and -svr- 



