27 



jj. Body not umcli compressed ; claw without tooth or with basal 

 tooth only, 

 k. Beak not produced much beyond first antennte. Oxyurella, 



Leydigia, Alona, Graptoleberis. 

 kk. Beak much longer than the first antennae. 



Alonella in part, and Rhynchotalona. 

 ii. Hind margin of shell much less than greatest depth. 

 j. Body noticeably longer than wide. 



P/curopus, Alonella in part, Dunlievfdia. 



jj. Body spherical or nearly so. 



k. Post abdomen short with prominent pre-anal angle ; shell 



without conspicuous projection on antero-ventral angle 



(fig. lo). Chydorus. 



kk. Post abdomen large, pre-anal angle not conspicuous (fig. 14). 



Alonella. 

 bb. Trunk limbs not leaf like ; mandible with palpus ; body not distinctly 

 segmented ; with caudal ftirca ; antennae large, used for locomotion ; 

 bivalve shell enclosing entire body. OSTRACODA. 



c. Last pair of trunk limbs bent backwards within the shell and not used 

 for locomotion. Cypridid.f,. 



About 12 eastern genera. Cypridopsis z'idua is most common. It 

 has a broad shell marked dorsally and laterally with 3 promin- 

 ent dark bands, (fig. 18). 

 cc. Last pair of trunk limbs directed downwards and used for locomotion. 



CVTHERID.5J. 

 The genus Liiiinicylhere is the only free swimming freshwater form 

 in our region. 



