Hershler, Robert. <br/><br/>
A review of the North American freshwater snail genus Pyrgulopsis (Hydrobiidae) 
Robert Hershler. 
 - Washington, D.C.  Smithsonian Institution Press  1994. 
 - iii, 115 p.  ill.  28 cm. 
 - Smithsonian contributions to zoology  610  no. 554 .
<br/><br/>Includes bibliographical references (p. 111-115). 
<br/><br/><label>LCCN: </label>93047246  
<br/><br/><label>Subjects--Topical Terms: </label><br/>Pyrgulopsis--Classification.--North America
<br/><br/><label>LC Class. No.: </label>QL1  QL430.5.H9  / .S54 no. 554 
<br/><br/><label>Dewey Class. No.: </label>591 s  594/.3