1885.] 6 Jo [Cope. 



Measurements. M. 



Length to vent 0365 



" " auricular meatus 0120 



of fore leg 0180 



Width of head behind orbits 0880 



Many specimens from Guatemala from Henry Hague, and one from 

 Yucatan from Arthur Schott. 



VI. A SYNOPSIS OF THE MEXICAN SPECIES OF THE GENUS 

 SCELOPORUS Wieg. 



The genus Sceloporus, as is well known, consists of terrestrial, and 

 therefore depressed thoracopleurous Iguanidae, with flat scales and dis- 

 tinct parietal scuta, and femoral pores, without preanal pores and gular 

 dermal fold or collar. Its especial habitat is Mexico and Central America, 

 the south-western parts of the United States and California. A single spe- 

 cies ranges over the entire eastern district of the Nearctic Realm. Outside 

 of the districts named it does not occur. 



The species are rather numerous, but their exact number has been 

 uncertain. It is with the view of determining this question that the pres- 

 ent investigation has been undertalien. Since Wiegmanri described the 

 most abundant of the Mexican species, synopses have been published by 

 Dumeril and Bibron and Bocourt. The latter author has published also, 

 in the Report of the Mission Scientifique of Mexico, most admirable plates 

 of many of the species. The material which has furnished the basis of the 

 present paper is largely the property of the National Museum of Wash- 

 ington. It has been furnished by the following naturalists : Messrs. 

 Riotte, Van Patten, Hague, Berendt, Sumichrast, Xantus, Sartorius, 

 Duges, Potts and Major. On my own part, I have received specimens 

 from Messrs. Duges, Hoege, Ferrari-Perez, Villada, Herrera and Bernad. 

 To all of these gentlemen I wish to extend my thanks for their kind atten- 

 tion in ^he matter. 



The distinction of many of the species of this genus is not accomplished 

 without difficulty. I recommend it as an excellent piece de resistance for 

 those persons who do not believe in the doctrine of derivation 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 pores, 

 and the granular lateral scales of some of the species. The carination and 

 wrinkling of the head-scales is frequently a valid character, but is espe- 

 cially unreliable in the S. undulatus, and one or two other species. The 

 size of the dorsal scales varies in most of the species ; the number enter- 

 ing 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 8.-torquatus. The longitudinal division of the 

 anterior frontal is constant in the 8. variabilis, S. siniferus and S. squamo- 



PROC. AMER. PHILOS. SOC. XXII. 130. 2x. PRINTED JULY 29, 1885. 



