588 BULLETIN 159, UNITED STATES NATIONAL MUSEUM 



44. Middle segment of first endopod with 2 inner setae; middle seta 



of fifth leg longer than outer one, both filiform; first antenna 

 12-segmented; fresh water, bottom form. 



d^ 9 Eucyclops Glaus, 1893 (p. 337) 

 Middle segment of first endopod with 1 inner seta; outer seta of 

 fifth leg longer than middle one ; metasome strongly flattened 45 



45. First antenna slender, 11-segmented, sparsely setose; caudal 



ramus twice as long as wide, with a dorsal transverse row of 



spines at its tip; fresh water, littoral 9 Heterocyclops Glaus, 1893 



First antenna stout, 8-segmented, densely setose; caudal ramus 

 five times as long as wide, without a dorsal transverse row of 

 spines; fresh water, bottom form- 9 Paracyclops Glaus, 1893 (p. 342) 



46. Fourth metasome segment produced on each side into a wing- 



like process larger than the body; second antenna with 2 api- 

 cal spines; gills of lobster 9 Nicothoe Audouin and Edwards, 1825 



No lateral processes on fourth segment; second antenna with 3 

 apical setae; first antenna 5-segmented, its aesthetask twice 

 as long as the antenna; littoral, moderate depths. 



9 Ratania Giesbrecht, 1892 



No lateral processes on fourth segment; second antenna with 



6 or 7 long curved apical setae 47 



47. Third and fourth metasome segments fused, dorsally over- 



lapping the fifth; endopod segments of first and second legs 

 flattened into broad laminae; on gills of fishes. 



cf 9 Artacolax Wilson, 1908 (p. 383) 

 Third and fourth metasome segments separated, no overlapping; 

 endopod segments of first and second legs like those of the 

 other 2 pairs 48 



48. Three basal segments of first antenna fused, enlarged, flattened, 



with dense fringe of setae; maxillipeds turned forward out- 

 side mouth parts; gills of fishes. 



& 9 Bomolochus (part) Nordmann, 1832 (p. 381) 



Basal segments of first antenna neither fused, enlarged, nor 

 flattened; second antenna greatly enlarged; maxillipeds 

 lacking in female; gills of fishes. 



cf 9 Ergasilus (part) Nordmann, 1832 (p. 375) 



Basal segments of first antenna neither fused, enlarged, nor 

 flattened; second antenna normal size; maxillipeds present in 

 their usual place behind the outer mouth parts 49 



49. End segment of fifth leg with 3 spines and 1 seta; second seg- 



ment of first endopod with 2 inner setae; caudal rami twice 



as long as wide; in brine pools 9 Neocyclops Gurney, 1927 



End segment of fifth leg with 2 setae, 1 apical and 1 inner 50 



End segment of fifth leg with 3 setae, or spines, or both 51 



End segment of fifth leg with 4 setae, or spines, or both 52 



50. Spines on end segment of exopods 2, 3, 3, 3; apical setae of 



fifth leg equal in length; lateral body margins not broken at 

 joints; fresh water, everywhere, c? 9 Mesocyclops G. O. Sars, 1914 (p. 330) 

 Spines on end segment of exopods 3, 4, 4, 4; apical setae of 

 fifth leg very unequal; lateral body margins broken or 

 notched at joints; fresh water, everywhere. 



d" 9 Cyclops (part) O. F. Muller, 1776 (p. 322) 



