246 MICROSCOPY FOR BEGINNERS. 



c. Smooth, brown ; spine on the lower angle. Sca- 



pholeberis, 2. 

 c. Reticulated; spine on the lower angle; antennae 



large, cylindrical. Bosmina, 3. 



c. Reticulated ; spine or tooth on the upper angle ; an- 



tennae long, witli two branches. Ceriodaphnia, 4. 



d. Beaked in front (e). 



d. Not beaked, oval, both ends rounded ; smooth or 



hairy. Cypris, 5. 



e. Posterior border with one to four small teeth. 



Camptocercus, 6. 



e. Posterior border without teeth (f). 



f. Shell nearly spherical ; posterior border truncate. 



Chydorus, 7. 



f. Shell not spherical ; posterior border convex ; an- 

 tennas small. Alonopsis, 8. 



f. Shell not spherical; posterior border truncate; 



antennae large, long, and branched. Sida, 9. 



g. Body long and narrow ; antennae long, twenty-five 



jointed. Didptomus, 10. 

 g. Body long and narrow ; antennae short, four to ten 



jointed. Canthocamptus, 11. 

 g. Body racket (battledoor) shaped, with two external 



ovaries. Cyclops, 12. 

 h. Body enclosed in a bivalve shell (). 

 A. Body not enclosed in a shell (/). 

 i. Shell nearly spherical, smooth. Limnetis, 13. 

 *'. Shell oval or oblong, flattened, amber-colored, with 



longitudinal lines. Estheria, 14. 



