122 BRITISH LIZARDS 



In the genus Phrynosoma, the so-called horned toads, 

 a striking change of colour due to age is seen in the 

 species P. coronatum. The young of both sexes have 

 short tails. The colour above is brownish, yellowish, 

 or greyish, darker laterally. There is a large brown 

 patch on each side of the neck, and a series of three 

 more or less distinct brown bars on each side of the 

 back. These bars are light-bordered posteriorly. The 

 tail is transversely banded with brown. The belly is 

 often dotted or blotched with brown or black. All 

 these colour markings are more distinct in the young 

 specimens than in old ones. In very young individuals 

 the scales on the top of the head are greyish or 

 yellowish white, with a few minute brown or black 

 spots. These spots, which are on the raised portions 

 of the scales, become more numerous as the animals 

 increase in size, i.e. in age, until the whole crown 

 appears black or dark brown, crossed by irregular lines 

 formed by the yellow posterior edges of the scales. 

 So that in P. coronatum the colour of any particular 

 specimen depends mainly upon the age. A closely 

 related species exemplifies the disappearance of mark- 

 ings in old age, namely, Anota platyrhina. In this 

 lizard the markings on the posterior part of the back 

 are apt to become obsolete in old specimens. It 

 frequently happens that the regular arrangement of 

 the colour pattern is appreciable only in the young. 

 An example of this is to be found in the Mexican 

 Heloderma su^j^ectum, a lizard of great interest, inas- 



