1906.] IN MEXICAN LIZARDS. 339 



be called O. gularis mexicamis, in opposition to C. giilaris com- 

 7mmis, but not possibly could it be named a race of communis. 



Lastly, on Cozumel Island, oiT Yucatan, C. communis reappears, 

 so that we may infer its occurrence in Yucatan. 



Cnemidophorus communis occidentalis. (Text-figs. 69, 77 A-F, 

 78 B, 79 A.) 



Diagnosis. — 4 supraoculars. Strong collar. Posterior side of 

 forearm with scutes or enlarged polygenes. Stripes bi"oken up, in 

 the adult, into rows of round spots ; fields with similar rows of 

 spots. Humeral rows of scales 5-7. Femoral rows 6-7, mostly 6. 

 Pores 16-21. ^ Length rarely exceeding 100 mm. 



Range the same as that of the Sierra Madre occidental, from 

 N.W. Chihuahua to Jalisco. 



Specimens from Ixtlan differ considerably in their colour- 

 pattern, approaching thereby C. mexicanas of Oaxaca — a very 

 significant case of convergence. 



On the Central plateau C commv,nis seems to remain somewhat 

 smaller, with less emphasised characters in coloration ; but it 

 reappears intensified at Puebla. Such an extension across the 

 country, from Jalisco, across Guadalajara towards and beyond 

 Guanajuato and Qaeretaro, conforms well with the physical 

 features of the country ; and in my paper on " The Distribution 

 of Mexican Amphibians and Reptiles," Proc. Zool. Soc. 1905 

 (vol. ii. p. 191), I have been able to show the existence of such an 

 exchange. Whether these Cnemidojyhori ascended thi'ough this 

 Jalisco gap, or descended thither from the plateau and from the 

 bases of the Westei-n Sierra Madre, is another question. 



Lake Santa Maria (text-fig. 78 B) in IST.W. Chihuahua. — The 

 single specimen is remarkable for having onl}^ 3 supraoculars on 

 the left side, whilst the 4th right is very small. The collar 

 consists of only one row of scales, which are rather small, and 

 neai'ly all of the same size. The posterior surface of the forearm 

 shows three roAvs of large polygenes, none of which can be called 

 large scutes. The other structural features likewise afford no 

 decided clue to the. affinity of this specimen. Throat and collar 

 are white, with a bluish tinge across the mid-throat and across 

 the collar excepting the row of larger scales. Chest and abdomen 

 white, with bluish bases to some of the scales. Tail, hind and 

 fore limbs, and anal region are white beneath. The upper 

 surface is uniformly slaty grey, rather dark, with many small 

 whitish specks, especially on the lower back, rump, thighs, and 

 root of tail. Of the original stripes, only faint traces of stripes 1 

 and 2 are still visible. 



The dusky band across the collar and the small whitish and 

 bluish dorsal spots undoubtedly point to the relationship of this 

 specimen with those of Tuxpan (text-fig. 79 A). 



Durango, from the foot of the Ii'on Mountain, on rather barren 

 ground (text-fig. 77 C). — Supraoculars 4. Collar composed of 

 large scales, mostly with an imperfect, once with a complete row 



Proc. Zool. Soc— 1906, Vol. I. No. XXIII. 23 



