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 



*''"■'''"" 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 posteriorly; t^ 

 surface smooth, the growth lines being indistinct; hinge 

 nearly straight; cardinal teeth small, the anterior tooth _^ 



being larger and more prominent; the lateral teeth not F,g_i8i pisidium 

 much elongated. abditum. x2 



Locality. Goat island. 



