28. Post-abdomen long and narrow with nearly parallel sides and with spines 



along the side getting larger at the end and about one-half the si2;e 

 of the terminal claw 



OxyureUa Dybowski & Grochowski 

 (Odonta]ona Birge) 

 Post-abdomen usually broad; with small spines of about equal si^e along 

 the side 29. 



29. Spines along the edge of post-abdomen usually smaller than the row just 



back from the edge, if these are present 



Alonella Sars 

 Spines along edge of post-abdomen usually larger than the row back from 

 the edge, about one-half or more the si2,e of the spine at the base of the 

 terminal claw 



Alona Baird (part) 



30. With a spine about the si^e of the basal spine of the terminal claw pro- 



jecting from the middle of the terminal claw on the post-abdomen 31. 

 Not so -^5. 



31. Rostrum very narrow and somewhat longer than antennules (not count- 



ing setae of antennules) 



Kurzia Dybowski & Grochowski 

 (Pseudalona Sars) 

 (Alonopsis of some writers) 

 Rostrum thick, about length of antennules 32. 



32. With a row of spines back from the edge of post-abdomen but no row 



along the edge 



Acroperus Baird 

 With a row of spines along edge of post-abdomen, with or without a row 

 back from the edge 33. 



33. Valves faintly marked with concentric lines; head small, with rostrum 



not descending half way down height of body 

 Euryalona Sars 

 Valves marked with lengthwise or oblique parallel lines; head large, with 

 rostrum descending below mid-line of height of body 34. 



34. With a dorsal crest; post-abdomen slender 



Camptocercus Baird 

 No dorsal crest; post-abdomen moderate to broad 

 Alonopsis Sars 



35. Body almost round 



Chydorus Leach 

 Body long oval or rectangular 36. 



36. With one spine at base of terminal claw on post-abdomen 



Rhynchotalona Norman 

 With two spines or with one spine and a bunch of spicules at base of 

 terminal claw- on post-abdomen 37. 



37. With one spine and a bunch of spicules at base of terminal claw 



Alona Baird (part) 

 With two spines at base of terminal claw 

 Pleuroxus Baird 



183 



