734 



FRESH-WATER BIOLOGY 



228 (226, 227) With one tooth on labrum; no spine on valves. 



Chydorus poppei Richard 1897. 



Like hybridus but without spine at infero-posteal 

 angle. Tooth on labrum sometimes small or obso- 

 lescent. 



Louisiana, California; rare. 



Very probably the last two species should be 

 listed as varieties of barroisi. These species were 

 first placed in Pleuroxus, but have no very close 

 affinity with either Pleuroxus or Chydorus; might 

 well be made a separate genus. 



FIG. 1157. Chydorus 



ai MM. 



229 (211) Post-abdomen large, pre-anal angle ordinarily not prominent. 



Alonella Sars 1862 . 



230 



This genus consists of a heterogeneous assemblage of forms; not assignable elsewhere and not 

 easily separable. There are 3 sections which might well constitute separate genera: 



(i) A lonella proper. Rostrum long, slender, recurved; usually conspicuously so; post- 

 abdomen with marginal denticles only; claws with i basal spine. A . rostrata, dadayi, 

 nana. (2) Paralonella. Rostrum short, hardly exceeding antennules; post-abdomen with 

 very small marginal denticles, with or without lateral fascicles; claws with i basal spine. 

 A. karua, denttfera, diaphana, globulosa. (3) Pleuroxalonella. Rostrum moderate; post- 

 abdomen with marginal denticles only; claws with 2 basal spines. Pleuroxus-like. A. 

 excisa, exigua. 



230 (235) Rostrum short; post-abdomen with marginal and lateral denticles. 



231 



231 (234) Valves with infero-posteal angle toothed 232 



232 (233) About 3 fine teeth; valves striated. . Alonella karua (King) 1853. 



General shape like Alona and easily 

 taken for a member of that genus. (See 

 152.) Valves with oblique striae; infero- 

 posteal angle with 1-4 minute teeth. 

 Post-abdomen broad, expanded behind 

 anus; apex rounded; with about 8 minute 

 marginal denticles and as many lateral 

 fascicles, much larger. Claws with i 

 small basal spine. Color yellow, trans- 

 parent. Length, ,0.45 mm; (South 

 America), 0.23 mm. 



Louisiana, Texas, Arkansas; not rare, 

 in pools and lakes. 



FIG. 1158. Alonella karua. 



CM MM. 



