. Bulletin - New York State Museum. Science. NIAGARA FALLS AND VICINITY 247 lower side of branches and floating debris, where they may be seen moving about by means of the long, flexible foot. Genus PisiDiuM Pfeififer. 1821 The animal closely resembles that of the foregoing genus, but the siphons are united to the end, those in S p h a e r i u m being separated and more elongated. The shell is trigonal or rounded oval; the cardinal teeth are very small and double, at times they are united and are situated directly under the beaks; the lateral teeth are elongated, lamelliform, double in the rig
. Bulletin - New York State Museum. Science. NIAGARA FALLS AND VICINITY 247 lower side of branches and floating debris, where they may be seen moving about by means of the long, flexible foot. Genus PisiDiuM Pfeififer. 1821 The animal closely resembles that of the foregoing genus, but the siphons are united to the end, those in S p h a e r i u m being separated and more elongated. The shell is trigonal or rounded oval; the cardinal teeth are very small and double, at times they are united and are situated directly under the beaks; the lateral teeth are elongated, lamelliform, double in the right valve, single in the left; the ligament is always on the shorter side. Pisidium virginicum (Gmelin) Bourg. 1853 (Fig. 179). T e 1 - lina virgin ica Gmelin (1788. ? p. 3236, pi. 159, fig. 15). Pisidium virginicum Bourg. (1853. Am. Malac. i :53) This is the largest Pisidium found in this region; it is thick and oblique; anterior side very much longer, ^ y o Fig. 179 Pisidium narrower and more rounded than the posterior side, ^'ii-g'ni'-'um. xs the latter being much broader and well rounded; beaks prominent and posterior; striae coarse; hinge broad and with twO' large cardinal teeth; laterals small and delicate. Locality. Goat island. Pisidium compressum Prime 1851 (Fig. 180). P. com press um Prime (1851. Bost. soc. nat. hist. Proc. 4:164) Shell solid, triangular and somewhat attenuated at *''"â '''"" the beaks, which are inflated; anterior side longer, Fig. 180 Pisidium narrow^cr and more produced than the posterior; the compressum. x5 , , , . , . \, , . latter subtruncate; beaks not much mtiated; striae distinct and regular; hinge thick, having strong, short teeth; cardi- nals compressed; laterals placed at an obtuse angle with the hinge. Locality. Goat island. Pisidium abditum Hald. 1841 (Fig. 181). P. abditum Haldeman (1841. Acad. nat. sci. Phil. Proc. 1:53) Shell rounded, oval and very thin, somewhat elon- f^ gated, beaks small, not inflated and placed post
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