MANUAL 



OF 



ONCHOLOGY; 



STRUCTURAL AND SYSTEMATIC. 



WITH ILLUSTRATIONS OF THE SPECIES. 



BY GEORGE W. TRYON, JR. 



CONTINUED BY 



HENRY A. PILSBRY. 



Vol. XIII. 



LEPETID.E, PATELLID/E, TITISCANIID.t. 



PHILADELPHIA : 

 Published by the Conchologieal Section, 



ACADEMY OF NATURAL SCIENCES, COR. igTH AND RACE STS. 

 1891. 



