Synopsis FrEsh-Water Mollusca 



29 



base, and with several basal denticles; laterals and marginals multicuspid. 

 Verge short, bifid, with a globular base. 



Type: Pahidina limosa Say, fig. 92. Animal, fig. 93. Operculum, fig. 94. 

 Radula, fig. 95. 



Fig. 95 



Fig. 96 



Subgenus CINCINNATIA Pilsbry, 1891. 



Radula more minute and the denticulations 

 of the cusps finer and sharper. 



Type : Pahidina cincinnatiensis Anth., fig. 96. 

 Radula, fig. 97. 



Genus PALUDESTRINA d'Orbigny, 1840. 



Fig. 97 



Shell similar to Amnicola, but more slender and elongated. 

 Central tooth with but one basal denticle on each side, and with- 

 out the tongue shaped process of Amnicola. Verge bifid. 



Fig. 98 



Fig. 99 

 Type: Cydostonia acntum Drap. 



Example: P. nickUniana (Lea), fig. 98. Radula, fig. 99. 



Genus TRYONIA Stimpson, 1865. 



Shell perforate, elongated, turreted, subulate ; apex acute ; 

 surface longitudinally ribbed or plicated ; whorls numerous, 

 shouldered ; aperture small, oblique, rhombo-ovate, lip sharp, 

 thin and effuse at the base ; peritreme continuous. 



Type : T. clatJirata Stimp., fig. 100. 



Genus PYRGULOPSIS Call and Pilsbry, 1886. 



Shell ovate-conical or turreted, imperforate, whorls having a single, 

 strong carina at the periphery, which may or may not be concealed on the 

 spire ; apex acute ; whorls 4^2 to 6 ; aperture ovate, peristome continuous ; 



Fig. 100 



