474 MR. G. A. BOULENGER ON THE [May 18, 



The following papers were read : — 



1. A Revision of the Lizards of the Genus Sceloporus. 

 By G. A. BouLENGER, F.R.S. 



[Eeceived March 29, 1897.] 



(Plate XXXin.) 



The discrimination of species in the genus Sceloporus is beset 

 with great difficulties. Cope has justly recommended it as "an 

 excellent pihce de resistance for those persons who do not believe 

 in the doctrine of derivation of species." The discrepancies 

 observable on comparing the revisions published about the same 

 time by Cope', myself", and Giinther'' show to what extent opinions 

 may differ on the delimitation of species. I have therefore con- 

 sidered it useful to undertake a renewed study of the genus, 

 embracing the whole material in the British Museum, which has 

 been greatly increased since the publication of the second volume 

 oE the Catalogue of Lizards, thanks chiefly to the donations of 

 Messrs. Salvin and Godman, Mr. W. Taylor, Dr. A. Dnges, 

 Mr. Van Denbiu'gh, and the collections made by Dr. A. C. BuUer 

 in Western Mexico and by Profs. Gilbert and Eigenmann in 

 California. 



1 have not restricted ray work to framing diagnoses, but have 

 drawn up tables of measurements and records of numbers of scales 

 and femoral pores * of nearly all the specimens, with the exception 

 of very young ones. These tables, I trust, will prove of more last- 

 ing value than systematic conceptions, and be of service to future 

 workers in the same field as well as to those who might wish to 

 test the constaucy of the characters on which species have hitherto 

 been established. 



Coloration, even the most conspicuous markings, I find generally 

 inconstant as a specific character, and liable more often to deceive 

 than to help in identifying specimens if considered previously to 

 the structural characters. Therefore, whilst paying to coloration 

 the attention which it deserves, I have abstained from introducing 

 any allusion to it in the key preceding the descriptions of the 

 species, all of which are based on structural characters. 



^ Proc. Amer. Philos. Soc. xxii. 1885. 



2 Cat. of Lizards, ii. 1885. 



3 Biol. C.-Araer., Rept., 1890. 



* These tables read as follows : — 



1. Length from snout to vent (in millimetres). 



2. Length of shielded part of head (from end of snout to posterior 



border of intei'parietal shield). 



3. Length of head to ear-opening. 



4. Length of tibia. 



6. Distance between base of fifth toe and extremitj' of fourth. 



6. Number of scales from occiput to base of tail. 



7. Number of scales corresponding to length of shielded part of head. 



8. Number of scales round middle of body. 



9. Number of femoral pores (right and left). 



