CROCODILIANS, LIZARDS, AND SNAKES. 333 



by DuiiK'ril aud Bibroii, Bocourt and myself. Bocourt has published 

 also, in the Report of the Mission Scientitique of Mexico, most admi- 

 rable plates of many of the species. I have given a synopsis of the 

 species,^ twenty nine in number. The material which has furnished 

 the basis of the ijresent work is largely the property of the U. S. 

 National Museum at Washington. It has been furnished by the follow- 

 ing naturalists: Messrs. Riotte, Van Patten, Hague, Berendt, Sumich- 

 rast, Xantus, Sartorius, Duges, Potts, and Major. On my own part, I 

 have received specimens from Messrs. Duges, Hoege, Ferrari-Perez, 

 Yillada, Herrera, and Beriiad. To all of these gentlemen I wish to 

 extend my thanks for their kind attention in the matter. 



The distinction of many of the species of this genus is not accom- 

 Ijlished without difticulty. 1 recommend it as an excellent ]}iece de 

 rhistance for those persons who do not believe in the doctrine of deriva- 

 tion of species. There are some characters, it is true, which are not 

 subject to such variation as to be embarrassing. Such are the greater 

 or less number of femoral j)ores, and the granular lateral scales of some 

 of the species. The carination and wrinkling of the head scales is fre- 

 quently a valid character, but is especially unreliable in the 8. undulatns, 

 and one or two other species. The size of the dorsal scales varies in 

 most of the species; the number entering a head length varying two to 

 three in the large-scaled spaces, and three or four in the small scaled 

 ones. The division of the supraocular plates into two or more rows is 

 constant in a few species only; in others it is variable, notably in the« 

 S. torquatus. The longitudinal division of the anterior frontal is con- 

 stant in the S. variahilis, S. siniferus, and /S'. squamosum, but is i)resent 

 or absent indifferently in several others. The number of sui^raoculars 

 in the principal row may be four or five in most of the species. 



The greatest difiBculty is experienced in distinguishing the North 

 American species. They are much fewer in number than has been rep- 

 resented to be the case, and the few that are admissible do not present 

 the strong characteristics that most of those of more southern regions 

 do. The S. undulaina has an almost continental distribution in North 

 America, within the range of temperate and subtropical climates. 



The arrangement of numerous species of the genus into groups is a 

 matter of much ditlficulty, owing to their gentle gradations of form and 

 the sometimes slight difference in color. The number and arrangement 

 of the supraorbital plates and the verticals furnish good characters, 

 though sometimes varying somewhat in the species. The arrangement 

 of the cervical jilates can not be relied on entirely for specific charac- 

 ters, although the average is much the same in the species. 



While the species of Sceloporus possess brilliant colors, these are gen- 

 erally on the inferior surfaces and are therefore concealed. The throat 

 and sides of the belly are usually of some shade of blue (sometimes 

 purple), while the dorsal regions are, in a majority of species, different 



'Proceedings of the Aiuericau Philosophical Society for 1885, p. 400. 



