26 



hh. Head without a beak, 

 i. First antenna of female very short, head small and depressed 

 (fig. 6). Ceriodaphnia. 



ii. First antenna large, head high. Moina. 



^^,. First antenna long ; often with 6 pairs of feet ; usually no hepatic 

 cseca. 

 h. First antennae large and fixed ; six pairs of feet (fig. ii). 



BoSMiNiD.^. Bosmina. 

 hh. First antennte long and freely movable. MACROTHRiCiDiS. 



i. Intestine convolute. 



j. Valves with spine at upper posterior angle. Ophvyoxus. 



jj. Spine absent, 

 k. Convolutions of intestine in middle of body. 



I. Dorsal margin of shell with conspicuous short backward 



pointing tooth about the middle. Drepanothrix. 



II. No dorsal tooth. Parophryoxiis. 

 kk. Convolutions of intestine in hind part of body. 



I. Posterior margin of shell truncated. A slight cervical sinus 



present. Acantholeberis. 



II. Posterior margin rounded with slightly pointed protuber- 



ance in middle. Streblocerus. 



ii. Intestine simple. 

 j. Upper posterior margin of shell truncated diagonally ; general 

 form oval-triangular, the head constituting the apex. Ven- 

 tral and posterior edges of valves enormously dilated and 

 rounded into each other, these having long close set setae 

 usually Ijranched and fringed. Ilyocryptus. 



jj. General form ovate, upper posterior margin of shell rounded, 

 not truncated. Setse on ventral margin of shell only, 

 k. Seta! long, movable, spine like and projecting in several 

 directions. ( fig. 9. ) Macrothrix. 



kk. Setse short and close set ; mid-posterior extremity forming 

 apex of roughly heart-shaped shell. Lathonura. 



ff. Second antennae with both branches three segmented. 



Chydorid.^. 

 g. Anus at extremity of post abdomen ; two hepatic coeca (fig. 7). 



Eurycerus laiiiellatus. 

 gg. Anus on dorsal side of post abdomen ; no hepatic coeca. 

 h. Head and back with high keel ; post abdomen very long and 

 slender ; with marginal and lateral teeth, (fig. 4). 



Caiiipfocerus. 

 hh. Not with all the above characters, 

 i. Hind margin of shell not much less than the greatest depth 



(height), 

 j. Body compressed ; claw on the concave side with one or two 

 teeth in the middle, 

 k. Shell with crest, R'urzia, and Acroperiis (fig. 8). 

 kk. No crest ; post abdomen with marginal and lateral teeth. 



Alonopsis, Eiirya/ona. 



