Introduction 



the Hylidae, the Pelobatidae, and the Ranidae. It resembles the 

 first in sometimes possessing adhesive disks on fingers and toes; 

 the second, in that the sacral diapophyses are in some species 

 dilated instead of cylindrical; the third, in nearly all ways, except 

 the fundamental one that it has a shoulder-girdle of the arciferous 

 instead of the firmisternal type. 



The various members of the family show habits aquatic or 

 terrestrial, burrowing or arboreal, and have proportions and struc- 

 tures adapting them to these various existences. The largest 

 number of species occurs in Mexico and Central and South Amer- 

 ica, but Australia is also well provided with them (twenty spe- 

 cies). Outside of these regions, the Family is not known, except 

 for the few forms found in North America, due to the overlapping 

 of the northern and southern zoological realms. North Ameri- 

 can genera are Lithodytes of Florida and Texas and Syrrophus 

 of Texas. (Refer to p. 163.) 



Family VI. Engystomatidce 



With some exceptions, these "Narrow-mouthed Toads" 

 have, as the name implies, a narrow pointed head and a small 

 mouth in sharp contradistinction from the type among the Sali- 

 entia. . t These structural characteristics of the family are related 

 to the habit of feeding upon ants and minute insects only. 

 The body is usually very stout, making the small size of the head 

 all the more striking. The ear is usually invisible. Most mem- 

 bers of the family possess no teeth on the jaw. There are never 

 palatine teeth, but often there is a serrated ridge across the roof 

 of the mouth in front and a second one farther back. These 

 ridges may 'be a modification in structure due to ant-eating 

 habits. 



The shoulder-girdle is always of the firmisternal type, but 

 it differs greatly among the various members of the family in its 

 details of structure. The pupil of the eye may be vertical, cir- 

 cular, or horizontal. The legs may be short or long; the toes 

 provided with disks or not. In fact, outside of the fundamental 

 distinguishing features (shoulder-girdle firmisternal, sacral dia- 

 pophyses dilated), there are few points of likeness among the 

 members of the family. Boulenger has divided it into three sub- 

 families, and the unlikenesses are evident also from the fact that 

 there are only about twice as many species as genera. 



10 



