1906. J IN MEXICAN LIZAKDS. 279 



as to the physical features. I have to thank the authorities of 

 that splendid museviin for their liberality in sending over to 

 Cambridge the greater number of their Cnemidopho7'i for minute 

 examination. These were svipplemented by the study of the 

 specimens in the British Museum, where, as usual, I had the 

 inestimable benefit of my friend Boulenger's critical advice and 

 never-failing help. Some Bei-lin types have also been examined. 

 The total of Cnemido2)hori studied for the purpose of this paper 

 amounts to some 520 specimens, from the United States to the 

 Isthmus of Tehuantepec ; about 450 of these are detailed in the 

 ajspended tables. Adding about 40 from South America in the 

 British Museum, studied cursorily for general comparison, the 

 whole amounts to some 560 specimens, apparently sufiicient for 

 all purposes, but in reality not so, since, for instance, the whole 

 iessellatus-gvoup is but meagrely represented. The whole range, 

 from the Isthmus to Utah, is enormous, more than 2000 miles ; 

 and even if we restrict oui'selves to Mexico, the 500 specimens are 

 crowded into compai'atively few disti-icts and leave many large 

 regions blank. Such a blank is, for instance, the country from 

 Colima to Acapulco, 300 miles. For the whole of Mexico proper, 

 excluding Yucatan and Lower California, scarcely 60 localities are 

 on safe record. A single locality, Hermosillo, represents the 

 whole large State of Sonora, and Presidio near Mazatlan the State 

 of Sinaloa. 



Mexico is an ideal country for the study of geographical distri- 

 bution, because it contains, often in juxtaposition, vast semi- 

 deserts, high plateavis, big continuous ranges of mountains with 

 peaks in the eternal snow, hot lowlands of the Atlantic or humid 

 type with luxurious rain forests, and of the Pacific or drier type ; 

 lai'ge forests of pines, oaks, or of tropical trees ; rivers and lakes ; 

 regions of enormous fertility and hopeless deserts. In short, 

 eveiy climate and every conceivable kind of bionomic conditions 

 are represented in this country. No wonder that this diversity 

 is expressed in the well-nigh endless, kaleidoscopic variations 

 of the genus Gnemidophorus, the main genus of strictly humi- 

 vagous Lizards of the countiy. 



This Tejid genus is invaluable for the study of variation. It is 

 so plastic within its well-defined generic characters, that it is repre- 

 sented by some form or other in almost every kind of terrain. Its 

 highest altitude above sea-level seems to be reached near 7000 feet, 

 as shown by its occurrence near Santa Fe in ISTew Mexico. In 

 Mexico its highest record is 7100 feet near Puebla; it is absent 

 in the Valley of Mexico, about 7400, and at Amecameca 8000 feet, 

 but it reappears at San Juan del Rio 6300, Celaya 5800, Acam- 

 baro 6000, Patzcuaro 6700, Durango 6200, Chihuahua 4700 feet. 

 These localities show that the lizards are not averse to moderate 

 altitudes, but all these places are situated on some kind of plateau. 

 On more isolated mountains the lizards seem to stop at a lower 

 level. For instance, on the eastern slopes of the Nevado de 

 Colima they stop at 5100, on the Cerro de San Felipe near 



