. Fresh-water biology. Freshwater biology. 730 FRESH-WATER BIOLOGY 208 (205) No spine at infero-posteal angle. . 209. 209 (210) Valves with conspicuous projection on antero-ventral margin. ' Anchistropus Sars 1862. Sole American species. . Anchistropus minor Birge 1893. Fonn globular. Ventral region tumid anteriorly and ventral margin of valves bent sharply away from each other about one-third way from front and the valve folded out into a hollow groove and tooth, which contains the strong hook of the first foot. Head large, bulging over eye, the fomices broad and forming a sort of flap-hke ro
. Fresh-water biology. Freshwater biology. 730 FRESH-WATER BIOLOGY 208 (205) No spine at infero-posteal angle. . 209. 209 (210) Valves with conspicuous projection on antero-ventral margin. ' Anchistropus Sars 1862. Sole American species. . Anchistropus minor Birge 1893. Fonn globular. Ventral region tumid anteriorly and ventral margin of valves bent sharply away from each other about one-third way from front and the valve folded out into a hollow groove and tooth, which contains the strong hook of the first foot. Head large, bulging over eye, the fomices broad and forming a sort of flap-hke rostrum, which can be closely pressed to the valves. Post-abdomen broad at base, pre-anal angle overhanging: rapidly narrow- ing toward apex, which is prolonged into a lobe; a few marginal spines. Claws with long, slender basal spine, denticulate or smooth. First foot of 9 with strong hook, toothed on concave side, which lies in groove formed by folding of valves. In A. minor, groove for hook of first foot near anterior part of valves; hook not large. Color brown- yellow. J unknown. Length, 5, ca. mm. Maine, Michigan, Wisconsin, Louisiana. Fig. 1146. Anchistropus minor. 210 (209) No such projection 211 211 (229) Post-abdomen ordinarily short with prominent pre-anal angle. Chydorus Leach 1843 . 213 Shape spherical or ovate. Posterior angles little marked; infero-posteal angle usually un- armed. Antennules short and thick. Rostrum long and acute. Post-abdomen usually short, broad, rarely long and narrow (C. globosus); apex rounded; with marginal denticles only or (C. globosus) with very fine lateral fascicles. Claws with 2 basal spines, the proximal often very minute, rarely absent. $ with short rostrum, thick antennule, hook on first foot, post-abdomet often very narrow. 212 (213) Post-abdomen, long, narrow, PleuroxusAike. Chydorus globosus Baird 1850. Almost spherical; valves smooth or reticulated, sometimes striated in front. Post-abdomen with small pre-anal angle; numerous
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectfreshwa, bookyear1918
