1905.] AMPHIBIANS AND REPTILES. 213 
Ctenosaura, and we will not discuss the question which of the two 
groups is the more primitive ; apparently the latter, but this can 
be contested. 
Crotaphytus, a typical old Northern Sonoran genus with several 
species in Western United States. C. wisliseni ranging from 
Oregon and Nevada into Sonora and Chihuahua; C’. collaris also 
into Nuevo Leon. 
Holbrookia, from Texas and California into the dry parts of 
Northern Mexico. H. maculata into North Sonora, H. texana to 
Monterey and Lerdo near Torreon. I found it running about 
swiftly on the almost barren shaly ground near El Paso. A. pro- 
pinqua from Texas to Presidio near Mazatlan. 
Uta, with most species in South-western United States and in 
Lower California. U. elegans from Utah to Texas and Sonora; 
U. stansburiana from Utah to Torreon. U. lateralis from Presidio 
and Tres Marias Islands and JU. bicarinata are Mexican, from 
Presidio to Tehuantepec, and everywhere between these places. 
Otherwise strictly confined to the western side of the plateau and 
the coast, it has entered the plateau at Cuernavaca and Puebla. 
J have almost invariably found it on the stems and branches of 
low trees, upon which they flatten themselves like arboreal 
Sceloporus; rather remarkable, since the other species are so 
decidedly dwellers on the sandy or stony ground. Very important 
is the occurrence of a species, U. auriculata, on the Revilla 
Gigedo Islands, 280 miles south of Cape Lucas, Lower Cali- 
fornia, and nearly 350 miles from the coast of Jalisco. This 
genus is typically Sonoran, with its centre around the Gulf of 
California. 
Phrynosoma, “ Animal rey,” or “ Camaleén,” or ‘ Escorpién.” 
The original centre of this genus is undoubtedly Sonoraland, 
whence it extends now over most of the Central, South-western, 
and Western States of North America and over the whole of 
Mexico as far as Guatemala. Ph. cornutwm, modestum, and 
orbiculare are, in Mexico, scattered over the plateau. Ph. asio 
is the most southern and at the same time the largest and most 
handsome species, ranging from Colima to Guatemala. Stejneger 
and Cope have already remarked on the ‘‘metachrosis” of 
Ph, douglasi. I have found Ph, modestwm near El Paso of 
exactly the same delicate French-grey colour as the little slabs 
of Cretaceous limestone with which the hills are strewn; the 
same species at San Marcial and at Rincon in Mexico, on the red 
and sandy voleanic rubble of that hilly desert region, were of the 
same pronounced red tint. Examination with a magnifying- 
glass showed the spirit-specimens to be covered with the iron- 
stained red sand, but those which I have brought home alive 
show this same red colour also to be that of their genuine skin. 
Sceloporus may well be called the most characteristic genus of 
Mexican Lizards. Of the 34 species recognised by Boulenger, 
28 occur in Mexico, between El] Paso and Tehuantepec. Only 
A live in the United States, and only 3 or 4 are found south of 
