16. Antennules immovable in female; end of body flattened, with a spine 



projecting backwards from junction of posterior and ventral margins; 

 Family Bosminidae 



Bosmina Baird 

 Antennules movable in female; posterior margin usually rounded or 

 pointed at top or middle; Family Macrothricidae (part) 17. 



17. Most of setae on antennae almost smooth or with a few spines or pro- 



cesses 



Macrothrix Baird 

 Setae feathery 



Lathonura Lilljeborg 



18. With long movable antennules projecting from tip of head; Family 



Macrothricidae (part) 19. 



Antennules usually short, projecting from behind a very pronounced 



beak; Family Chydoridae 23, 



19. Coil of intestine in posterior end of body, partly in the post-abdomen 20, 

 Coil of intestine in about the middle of the body 21, 



20. With a flattened posterior margin 



Acantho/eberis Lilljeborg 

 With a rounded or pointed posterior margin 

 Strehlocerus Sars 



21. Posterior margin rounded; dorsal margin with a backwards projection in 



about the middle 



Drepanothrix Sars 

 Posterior margin rounded or tube-like; dorsal margin even 22, 



22. Upper part of posterior margin pointed 



Ophryoxus Sars 

 Posterior margin drawn out into a short tube 

 Parophryoxus Doolittle 



23. Intestine ending at the end of the post-abdomen 



Eurycercus Baird 

 Intestine ending well up on the post-abdomen 24, 



24. Rostrum not projecting downwards beyond antennules; each of two claws 



on post-abdomen with one or no spines 25. 



Rostrum distinctly longer, or else claw on post-abdomen with two or 



more spines, or both 30, 



25. Post-abdomen large, wide, and with numerous large spines 



Leydigia Kur^ 

 Post-abdomen narrow or with short spines 26, 



26. Anterior margin of head and beak very slightly incurved or almost straight 



Graptoleheris Sars 

 Anterior margin of head and beak curving outwards 27. 



27. Post-abdomen bent abruptly outwards and about twice as wide below 



end of intestine 



Dunhevedia King 

 Post-abdomen not abruptly much wider below end of intestine 28, 



182 



