AMPHIBIANS 



175 



water only in the spring time to breed; maxillary and vomerine teeth 

 present; no parotoid glands; digits expanded at their tips to form 

 glandular disks, the sticky secretion of which assists the animal in 

 climbing; front toes sometimes slightly webbed, hind toes usually fully 

 webbed; eggs of American species laid in small masses in the water: 

 about 190 species, most of which are in the Neotropic region; 18 species 

 in the United States, which often show a remarkable metachrosis. 



Key to the United States Genera of Hylidae 



ai Finger and toe disks conspicuous (Fig. 88) i. Hyla. 



a2 Finger and toe disks very small (Fig. 89). 



bi Hind toes fully webbed 2. Acris. 



bo Hind toes slightly webbed 3. Pseudacris. 



Fig. 88. — Hind and fore foot of Hyla versicolor 

 (from Surface). 



J. — Hind and fore foot of Acris 

 grylhis {frotn Surface). 



I. Hyla Laurenti. Hind toes webbed; skin smooth in most species; 

 belly granulated; pupil round or horizontal: about 10 species in the 

 United States. 



Key to the United States Species of Hyla 



ai In the States east of the Rockies. 



bi In the eastern and central States north of the Gulf States. 



Ci Fingers somewhat webbed; skin rough, warty H. versicolor. 



c-: Fingers entirely free of webb; skin smooth. 



di Back with an oblique cross-shaped marking H. crucifer. 



dz Back plain, without markings, but sometimes with spots, 

 ei Color on the back without a definite lateral margin. 



fi No light line on side of the slender head H. evittata. 



fo A light line on the upper jaw (sometimes indis- 

 tinct) ; head stout H. squirella. 



