734 



FRESH-WATER BIOLOGY 



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



Chydorus poppei Richard 1897. 



Like hyhridus 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 verj^ close 

 afl&nity with either Pleuroxus or Chydorus; might 

 well be made a separate genus. 



Fig. 1157. Chydorus poppet. 



aiMM. 



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) y4/o?je//a 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, dentifera, diaphana, glohiilosa. (3) Pleuroxalonella. Rostrum moderate; post- 

 abdomen with marginal denticles only; claws with 2 basal spines. Pleuroxus-likt. 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 rovmded; with about 8 minute 

 marginal denticles and as many lateral 

 fascicles, much larger. Claws with i 

 small basal spine. Color yellow, trans- 

 parent. Length, 9, 0.45 mm; $ (South 

 America), 0.23 mm. 



Louisiana, Texas, Arkansas; not rare, 

 in pools and lakes. 



Fig. 1158. Alonella karua. 



0.i MM. 



