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Show 1 9 0 5 .] AMPHIBIANS AND REPTILES. 2 1 3 Ctenoscmra, 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. wislizeni ranging from Oregon and Nevada into Sonora and Chihuahua; C. collaris also into Nuevo Leon. llolbrookia, from Texas and California into the dry parts of Northern Mexico. II. metadata 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. H.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. stausburiana from Utah to Torreon. U. lateralis from Presidio and Tres Marias Islands and U. 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. I 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 California, 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 " Camaleon," or " Escorpion." 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. cornutum, mode stum, and orbicidare 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. modestum 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 volcanic 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 4 live in the United States, and only 3 or 4 are found south of |