12. With ten or eleven segments in first antennae 



Ectocyclops Brady 

 With twelve segments in the first antennae 

 Eucyclops Claus 



13. With two plumes from the end of the fifth leg 



Mesocyclops Sars 

 With one plume and one or two spines from the end of the fifth leg 14. 



14. With one plume and one spine from the end of the fifth leg 



Cyclops Miiller 

 With one plume and two spines from the end of the fifth leg 

 Macrocyclops Claus 



GENERAL REFERENCES 



Coker, R. E. 1934. Contribution to Knowledge of North American Fresh- 

 water Harpacticoid Copepod Crustacea. Jour. Elisha Mitchell Scientific 

 Soc, Vol. 50, Nos. 1 and 2. Chapel Hill ,N. C. 



Forbes, E. B. 1897. A Contribution to a Knowledge of North American 

 Fresh-water Cyclopidae. Bull. 111. Lab. Nat. Hist., Vol. 5. 



Herrick, C. L. and Turner, C. H. 1895. Synopsis of the Entomostraca of 

 Minnesota. Second Report of the State Zoologist. Geol. and Nat. Hist. 

 Surv. of Minn. 



Marsh, C. D. 1918. Copepoda. Chap. 23 in Ward and Whipple's ''Fresh- 

 water Biology". John Wiley 6? Sons. New York. 



Wilson, C. B. 1903. North American Parasitic Copepods of the Family 

 Argulidae. Proc. U. S. Nat. Museum, Vol. 25. 



Wilson, C. B. 1911. North American Parasitic Copepods Belonging to the 

 Family Ergasilidae. Proc. U. S. Nat. Museum, Vol. 39. 



KEY TO THE COMMON GENERA OF AMPHIPODS 

 OR SCUDS 



1. Last pair of peraeopods (legs on thora.x) shorter than the preceding pair; 



Family Lysianassidae 



Pontoporeia Kroyer 

 Last pair of peraeopods longer than the preceding pair 2. 



2. Telson not spHt 3. 

 Telson (central posterior appendage) partly or wholly split lengthwise 



Family Gammaridae 4. 



3. First pair of antennae without any small branch portion; with functional 



eyes; in rivers, ponds etc. ; Family Talitridae 

 Hyalella Smith 

 First pair of antennae with one very short branch from middle or from 

 near end; blind; in caves or wells 



Crangonyx Bate (of Family Gammaridae) 



4. Telson almost wholly or completely split 



Gammarus Fabricius 

 Telson split not more than three-quarters of its length 5. 



187 



