446 Illinois State Laboratory of Natural History. 



power of swimming, the animal creeps along the bot- 

 tom — a very different habit from that of Cypris. 



Twelve species are known, two of which were described 

 from America. An analytical table of the species occurring 

 or likely to occur in this country is inserted here for the 

 convenience of workers. I have examined none but E. 

 harbatus (Forbes). 



KEY TO SPECIES OF ERPETOCYPRIS. 



1 (7). Caudal rami with two terminal claws and a ter- 



minal and dorsal seta. 



2 (3, 6). Claw on last segment of second foot as long as 



segment. Shell about twice as long as high. Caudal 

 rami about ten times as long as wide, dorsal margin 

 finely toothed; dorsal seta not more than once width 

 of ramus from subterminal claw. 



E. STRiGATA (O. F. Miiller). 



3 (2, 6). Claw on last segment of second foot three 



times as long as last segment. 



4 (5). Dorsal seta of caudal ramus delicate, undevel- 



oped, close to subterminal claw; dorsal edge of ramus 

 armed with five combs of teeth; terminal seta fully 

 as long as subterminal claw. Shell somewhat longer 

 than twice its height, the upper and lower edges 

 nearly parallel. E. reptans (Baird). 



5 (4). Dorsal seta of caudal ramus transformed into a 



short spine or claw, close beside the subterminal 

 claw ; dorsal edge of ramus armed with an unbroken 

 row of fine teeth ; terminal seta three fourths as long 

 as the subterminal claw. Shell seven thirteenths as 

 high as long, the upper edge evenly convex, the under 

 edge very weakly concave. 



E. OLivACEA Bradj^ & Norman. 



6 (2, 8). Claw^ on last segment of second foot seven 



eighths as long as last segment. Dorsal seta serrate 

 and claw-like, close to subterminal claw; dorsal edge 

 of ramus finely toothed; ramus twenty times as 

 long as wide; terminal seta about a third as long 



