which the amateur can help solve hy observations in his own home territory. 

 A good indication of the need for study on frogs is the fact that even in the 

 southeastern states, where biologists have lived and studied for over two hun' 

 dred and fifty years, two species of frogs, both of good size and one almost as 

 large as the bullfrog, were overlooked and not even named until very recently 

 (Hyla avxvoca by Viosca in 1931 and Kana hec\scheri by Wright in 1924). 

 The characters used in the key need little explanation. 



LENGTH 



This measurement is of the head and trunk, the hind legs not being in- 

 cluded. Length of the head is taken from the tip of the snout to the rear 

 margin of the tympanum. 



HEAD 



On the side of the head, behind the eye, is usually a smooth disc, the 

 tympanuyn, tympanic membrane, or ear drum. Amphibians have no outer 

 chamber to the ear. On top of the head in some forms are two structures 

 useful in identification. One of these, present in the Bufonidae and most 

 Scaphiopodidae, consists of a pair of elevated glands, the parotoids. They, 

 with other glands, secrete a bitter fluid Vv'hich protects the possessor from many 

 enemies who might otherwise eat him. Some snakes devour toads in spite 

 of this protection, however. The other head character, developed only in 

 some of the Bufonidae, consists of cranial crests or raised folds of skin on the 

 top of the head and sometimes extending behind the eyes. The shape of the 

 eye pupil is a useful character in the identification of living specimens but seb 

 dom of value with preserved ones. The Scaphiopodidae have contractile pupils, 

 which close vertically in the daytime like those of a cat. The Ascaphidae, also, 

 have elliptically vertical pupils. The other frogs and toads have elliptically 

 horizontal pupils. 



TRUNK 



The surface of the ventral side — granular in most climbing frogs and in 

 the toads, smooth in most aquatic frogs — aids in identification. In some of the 

 Ranidae preservation may bring out granules that do not appear on the living 

 animals. The Ranidae are relatively smooth bellied and have no toe discs, a 

 combination of characters that sets them apart from most other frogs. The 

 dorsolateral ridges, folds of skin separating the back from the sides, vary in 

 their degree of development. For example, in the m.eadow frog these folds 

 run the full length of the trunk, in the green frog they extend about halfway 

 back, and in the bullfrog they are not developed at all. 



LEGS 



The enlarged thumb on the forelimb of the male Ranidae is characteristic 



336 



