Crustacea 



63 



30 — Hind margin of shell not much less than greatest depth 31 



— Hind margin of shell much less than greatest depth 32 



31 — Body compressed; claw on the concave side with one or two teeth in the middle. 

 Shell with crest, — Kurzia, and Acroperus (fig. 8); no crest, post abdomen with 



marginal and lateral teeth Alonopsis, Euryalona 



— Body not much compressed; claw without tooth or with basal tooth only. Beak not 

 produced much beyond first antennae — Oxyruella, Leydigia, Alona, Graptoleberis; 

 beak much longer than the first antennae — Alonella in part and Rhynchotalona. 



32 — Body noticeably longer than wide-Pleuropus, Alonella in part Dunhevedia 



— Body spherical or nearly so 33 



33 — Post abdomen short with prominent pre-anal angle (fig. 10) Chydonis 



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



34 — Last pair of trunk limbs bent backwards within the shell and not used for locomotion. 

 Cyprididae. About 12 eastern genera. Cypridopsis vidua is most common. It 

 has a broad shell marked dorsally and laterally with three prominent dark bands 

 (fig. 18). 



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

 The genus Llmnicythere is a free swimming freshwater form. 



