Hershler, Robert <br/><br/>
A review of the North American freshwater snail genus Pyrgulopsis (Hydrobiidae) 
Robert Hershler 
 - Washington  Smithsonian Institution Press  1994 
 - 115 p. : ill. ; 28 cm. 
 - Smithsonian contributions to zoology  no. 554 .
<br/><br/><label>LCCN: </label>93-47246 
<br/><br/><label>Subjects--Topical Terms: </label><br/>Pyrgulopsis--North America--Classification