4ii0 Illinois State Laboratory of Natural History. 



17 (18). Natatory setae of the second antennae well de- 

 veloped, plumose, reaching considerably beyond the 

 terminal claws. Anterior and posterior ventral mar- 

 gins of right valve generally armed with a row of 

 tuberculiform teeth. III. Cyphinotus. 



18 (17). Natatory setae of the second antennae not 

 well developed, commonly simple, and not reaching 

 bevond terminal claws. Margins of rio-ht valve not 

 armed with a row of tuberculiform teeth. 



19 (20). Natatory setae small or rudimentary, not 

 adapted for swimming. VI. Erpetocypris. 



20 (19). Natatory setae reaching to, or barely beyond, 

 the tips of the terminal claws. 



21 (22). Dorsal setae of caudal ramus rudimentary or 

 absent. Claws denticulate. VII. Stenocypris, 



22 (21). Dorsal setae of caudal ramus developed as usual, 

 and near claws. 



23 (24;). Caudal rami exceedingly large and elongate. 



V. Cypricercus. 



24 (23). Caudal rami, as usual, not disproportionately 

 developed. IV. Cypris. 



Descriptions of each of the above genera are inserted 

 throughout the text for the convenience of workers, al- 

 though but eight of the fourteen have been found in 

 America. 



The keys inserted are intended to be little more than 

 an analysis of the species mentioned in this paper. 



I. NOTODROMAS LlLLJEBGRG. 



1792. Cypm, 0. F. Muller (49, p. 48). 



1853. Notodromas, Lilljeborg (39, p. 94). 



1854. Cyprois, Zenker (75, p. 80). 



The second pair of antennae are six-segmented in both 

 male and female. The second maxilla lacks a branchial 

 plate. The palp of the female is two-segmented, the 

 terminal segment ending in two short setae. In the male 

 ^■his termiiinl spo-mfiir i^ morlifioi] into n liook-sliaped 



