280 



DR. H. GADOW ON EVOLUTION 



[Mar. 20, 



Oaxaca at 5400, whilst they are swarming at 5200 feet level. Near 

 Chilpancingo they do not go beyond 4500 feet. I suspect that they 

 are stopped by those changes which on so many mountains coincide 

 with the usual lowest level of the clouds. 



Although frequently found in ravines and on the spurs of 

 mountain-ranges, they avoid the mountains themselves, and above 

 all they are averse to crossing a system of cut-up ridges even of 

 moderate height. 



Some species, C deppei, immutabilis, and giMatus, are natives 

 of the Tieira caliente, which they do not leave, so that any con- 

 tinuous rise beyond 3000 feet is to them an absolute barrier. 

 When, by the way. Cope mentions C. deppei from Guadalajara, 

 this certainly cannot refer to the plain of 5000 feet upon which 

 this town lies, but to the deep depression of the neighbouring 

 Rio de Santiago, 2000 and more feet lower ! 



Southern, tropical species do not ascend far; but northernei'S, or 

 let us say highlanders, extend their i-ange frequently into the 

 lower, tropical climes, and thei-eby they undergo considerable 

 changes. 



It was stated that these lizards are very plastic. There are 

 some sjDecies which average only 50 mm., while others reach a nose 

 to vent length of 140 mm. 



I have selected only a few characters, chiefly the suprnoculars, 

 the composition of the collar, the rows of scales of the humerus, 



Text-fiL^ 61. 



Lcpidosis of tlio front of tlie left foroavni of Cnemidophorus mexicantis. 



A, B. Two specimens from Cueniavaca. C. From Balsas No. 2. D. Cuer- 



navaca No. 8. 

 E-I. Diagrammatic; I, an arrangement occurring in Cueniavaca No. 6 and 



Rincon No. 2. 



