Wingard, G. Lynn <br/><br/>
A detailed taxonomy of Upper Cretaceous and Lower Tertiary Crassatellidae in the eastern United States ; an example of the nature of extinction at the boundary / 
by G. Lynn Wingard 
 - Washington :  U.S. Government Printing Office,  1993 
 - 131 p. :  ill. ;  28 cm. 
 - U.S. Geological Survey professional paper ;  1535 .