Rana Onca 



Structure: Skin smooth, except for lateral folds and a few 

 inconspicuous elongated wart-like elevations on the back between 

 the lateral folds and on the sides. Head rounded, thick through, 

 with much the proportions and appearance of the head of Rana 

 clamitans. (Fig. 257.) Ear larger than eye in male, slightly 

 smaller than eye in female. No conspicuous ridge over ear. 

 No glandular fold along jaw. Feet delicate; webs broad and 

 long. Inner sole tubercle small; outer lacking. 



Range: Rana onca Cope is reported from Utah and Nevada. 



This species of frog (Fig. 257 and Colour Plate II) is not 

 nearly related to the black-cheeked frogs of the Pacific Slope. 

 It is apparently much nearer the eastern Rana clamitans, and the 

 spotted frogs Rana pipiens. The general colouring, also the 

 shape and proportions of head, body, and legs are remarkably 

 like those of Rana clamitans (Fig. 230); the spotting reminds 

 one of Rana pipiens (Fig. 197), but differs in that it represents 

 a temporary colour pattern instead of a permanent one. Rana 

 onca never attains the size of either of these other frogs. 



Rana onca is a very bright, active little frog. It eats worms 

 and insects greedily. It will try to take a worm away from a 

 companion frog, biting at the frog's head again and again. In 

 locomotion it proceeds by short hops, given in quick succession 

 with short toad-like legs. 



The power for rapid change of colour is considerable. The 

 frog may be brown or green, of light or dark shade. The spots 

 may or may not be rimmed with light colour. They may be 

 darker or lighter than the background of colour. When lighter, 

 they are shining gold or bronze. There is much iridescence in 

 the colouration. In fact, the young frogs may wear a coat 

 everywhere rich in metallic lustre. 



The frogs examined have shown no external vocal pouches. 

 The large webs and the unusually large tympanum make this 

 frog easy of indentification within its western range. 



197 



