THE WATER FLEAS (CLADOCERA) 



723 



IS7 (156) With marginal and lateral denticles. 



158 



158 (161) Size large; 14 or more marginal denticles 159 



159 (160) Cluster of fine spinules at base of claw. 



O.r MM. 



Alona affinis (Leydig) i860. 



Greatest height usually near middle of 

 valves. Valves longitudinally striated or re- 

 ticulated, often not plainly marked. Labrum 

 with rhomboidal keel; its corners often angu- 

 lated, sometimes rounded. Post-abdomen 

 large, not widened behind anus; with 14-16 

 serrate marginal denticles and a lateral row 

 of small squamae. Claws long, denticulate; 

 with long basal spine and 4-5 spinules inside 

 of basal spine. Six pairs of feet, the last rudi- 

 mentary. Length, 9jtoi.omm.; ^, to 0.7 

 mm. 



The largest species of the genus; very abun- 

 dant in all regions, in margin of ponds and 

 lakes, among weeds. 



Fig 1130. Alona affinis. 



160 (159) No spinules at base of claws. 



Alona quadrangularis (O. F. Miiller) 1785. 



Greatest height usually posterior to middle of valves. Valves usually plainly striated, 

 sometimes conspicuously so, with a reticulated area in infero-anterior region (var.lepida Birge). 

 Labrum with large keel of variable form; often quadrate or with rounded angles. Post-abdo- 

 men large, flattened, dorsal margin dilated; with 13-18 serrate marginal denticles and row of 

 lateral squamae. Claws large, with long basal spine; no spinules on inside of basal spine. 

 Length, 9,to 0.9 mm.; ^,to 0.6 mm. See Fig. 1129, a. In similar locaUties to preceding 

 species; also on bottom of open water. 



161 (158) Size moderate or small. Fewer than 14 denticles 162 



This section of the genus needs much additional study, 

 varieties beside those listed. 



There are species and numerous 



162 (163) Lateral fascicles or squamae do not extend beyond dorsal margin 

 of post-abdomen. . ... . . Alona cosiata Sars 1862. 



Evenly arched or greatest height behind middle; posterior margin convex. Valves striated 

 or smooth. Post-abdomen short, broad; with straight dorsal (lower) margin, tapering toward 

 apex; with about 12 subequal denticles and a row of fine squamae. Post-abdomen of $ taper- 

 ing; no marginal denticles; very fine squamae; vas deferens opens at apex of process 

 extending out ventral to (above) claws; claws without basal spine. Length, 9 , 0.5 mm. or 

 more; ^,0.4 mm. See Fig. 11 29, e. 



Found everywhere and very abundant. 



163 (162) Lateral fascicles long, extending beyond dorsal margin. 



164 



164 (165) Post-abdomen not broadened toward apex. 



Alona rectangula Sars 1861. 



Body evenly arched; general form like A. guttata. Valves striated, reticulated, or smooth, 

 rarely tuberculate; ventral margin usually somewhat convex. Post-abdomen short, shghtly 

 enlarged toward apex, angle rounded; with 8-9 marginal denticles or bundles of setae and about 

 as many fascicles, the distal long enough to project beyond margin of post-abdomen. Intestine 

 without cecum, enlarged at junction of intestine and rectum, somewhat as in Ilyocryptus, 

 Length, 9 , 0.35 to 0.42 mm. See Fig. 1129, e, /. 



Common everywhere. Most specimens found belong to var. fulchra Helljcb, 



