. Fresh-water biology. Freshwater biology. 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 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 lo
. Fresh-water biology. Freshwater biology. 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 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, ; ^, to 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 ( 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 mm.; ^,to 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 straig
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectfreshwa, bookyear1918
