6 BUFONOIDEA. 
of evening, and are truly nocturnal in their mode of life. This family has been 
arranged in several genera, characterized by the form and structure of the tongue; 
the number of toes, palmated or not; tympanum visible or not; tubercle at heel, 
&c. &c. Two of these genera have only yet been observed in the United States 
—Bufo and Engystoma. 
