Amphibians aud Reptiles of Mexico. 315 



dermal structure that is supported anteriorly by tlie extension of 

 the bony crest that rises from the parietal region of the skull. In 

 a male 642 mm long the dermal flap is 2H mm long from the 

 anterior end on the neck to the tip. In the young males between 

 400 and 450 mm in length the bony ridge is just beginning- to show 

 externally as a ridge, but the dermal part of the crest is quite well 

 developed, while in the females of the same size the dermal fold is 

 quite small. Tlie variations in the dorsal crest are somewhat different 

 for, whereas in the adult males it is relatively well developed 

 (13 mm at the highest point in a specimen 642 mm long) and is 

 very low in the adult females, in the young specimens between 

 400 and 450 mm it is very low and about equally developed in 

 both sexes. 



In color our specimens show much less variability than one 

 would expect from some of the published descriptions. In specimens 

 of both sexes and various ages (length 144 to 645 mm) the ground 

 color above is olive with more or less of a yellow finge (193, 212 

 and 262), becoming brown (179) above the upper stripe. The stripes 

 are usually dull on the body (143, 163 and 172), but in the smallest 

 specimen (144 mm) the lower one is bright througliout its length. 

 In some specimens the stripes are also dull upon the head and 

 neck, but they are as offen decidedly lighter. being some shade of 

 yellow (227, 246 and 256) or even wliite. The same is true of the 

 stripe that is usually found on the middle of the head. In the 

 only very small specimen (144 mm in length) that w^e have. the 

 stripes are white on the head and neck, the median head stripe 

 being also well developed. In none of the older specimens are 

 these stripes so bright, but in some of the largest individuals they 

 are lighter than in the medium sized ones. The black cross bars 

 are very distinct in all our specimens except in some of the oldest 

 males, in which they are broken up. The ventral surface is a pale 

 yellow in every specimen. On the belly there are small patches of 

 pale slate or pale brown, and the throat and chin are much blotched 

 with these colors, in some specimens to the nearly complete exclusion 

 of the yellow ground color. In several old males the belly is 

 washed with dull red (53d and 53b), but none of the males examined 

 had any red on the crest or tail as stated by Sümichrast.^) 



We found the Basüiscus a common lizard along the streams and 



1) in: Ann. Mag. nat. Hist., Vol. 13, 1864, p. 505. 



