Key to Cyclops species of the Laurentian Great Lakes:

1a. Long setules present on proximalmost seta of mxl palp (Fig. 5b)................................................ 2

1b. Long setules absent on proximalmost seta of mxl palp (Fig. 2b)................................................. 3

2. A1 extending beyond cephalothorax (female) and A1 first segment densely pitted (Fig. 3b), surface of mxl palp ornamented with large spinules (Fig. 5b), mxp syncoxopodite with short membranous element featuring prominent distal hook (Fig. 4b) and transverse row of small spinules, P1 basipodite medial spine with heteronomous setulation (Fig. 4c), P3 coupler unornamented, P4 coupler ornamented with horizontal row of long hairs (Fig. 5c), P4 coxopodite ornamented with spinules at positions A, C, D, and E (Fig. 4d), P4 coxopodite setae extending beyond medial margin of the basipodite (Fig. 4e), P5 basal segment lacking ornamentation................................................................. C. divergens Lindberg, 1936

3a. P4 coxopodite setae unmodified (Fig. 2f).................................................................. 4

3b. P4 coxopodite setae proximally swollen................................................................ 5

4. A1not extending beyond cephalothorax (female) andA1 first segment lacking pits (Fig. 1b), surface of the mxl palp unornamented or ornamented with only tiny spinules (Fig. 2b), mxp syncoxopodite with long membranous element featuring somewhat club shaped distal terminus (Fig. 2c) and transverse row of small spinules, P1 basipodite medial spine proximal margin bare (Fig. 2d), P3 and P4 coupler ornamented with horizontal row of long hairs, P4 coxopodite ornamented with spinules at positions A, B, C, D, and E (Fig. 2e), P4 coxopodite setae not extending beyond medial margin of the basipodite (Fig. 2f), P5 basal segment ornamented with spinules near insertion of lateral seta.................................... C. sibiricus Lindberg, 1949

5. A1 extending beyond cephalothorax (female) and A1 first segment lacking pits, surface of the mxl palp ornamented with small spinules, mxp syncoxopodite with short membranous element lacking distal hook or club and with oblique row of long spinules, P4 coupler unornamented, P4 coxopodite ornamented with spinules at positions A, B, C, D, and occasionally F, P4 coxopodite setae extending beyond medial margin of the basipodite, P5 basal segment unornamented............ C. scutifer Sars, 1863