346 DR. H. GADOW ON EVOLUTION [Mar. 20, 



inu7ns and lead on to the Pnebla clan, in wliicli the characters of 

 C. comormnis are again intensified. 



There is still a gap between San Juan del Rio and Puebla, 

 a distance of 150 miles, whence no Cnemidojyhori have been 

 recorded. I myself have never seen a single specimen in the 

 Yalley of Mexico, an absence due no doubt to the high eleva- 

 tion, the limit for this genus being apparently near 7100 feet. 

 Dr. Meek found them in abundance near Puebla, 7100 feet, 

 but the Capital, itself in the depression of the so-called valley, lies 

 some 300 feet higher. San Juan's elevation is 6000 feet, and 

 any way thence to Puebla would imply an ascent of more than 

 8000 feet, an elevation which may well be prohibitive to any 

 species of Cnemidopliorus. At Amecameca,' which lies at this 

 altitude, I looked for them in vain. It is therefore more likely 

 that the Puebla clan have arrived there by some roundabout 

 way at present unknown. But it is cei-tain that there is no 

 communication between them and those of Yautepec and Cuantla 

 in Morelos, although the distance would be less than 40 miles. 



Consequently it seems i-athei- likely that the spotted clan at 

 Puebla, with its isolation from the other C. coinmunis, represents 

 a case of convergent evolution. G. c. balsas itself is a case of 

 isolation ; they are i-estiicted to the basin of the Balsas, bounded 

 on the north by the impassable barrier of high mountains, the 

 southern fringe of the Central plateau, and on the sovith by the 

 Sierra Madre del Sur, the low j)ass of which, at Los Cajones, 

 these lizards just manage to .cross, but they do not descend 

 beyond, into the Coastal region. What happens to these Cneini- 

 dophori in Western Michoacan, whether they change or not, 

 into the western form, remains for the present vniknown. Tlie 

 same applies to the zoologically undiscovered wide districts of 

 the upper basin of the Balsas. 



Cnemidophorus communis copei. (Text-figs. 78 A, C, E.) 



Diffeidng from G. communis occidentcdls by the increased number 

 of humeial and femoral rows, greater number of pores, and larger 

 size of the body. 



Although these are difiei'ences of degree only, they are signi- 

 ficant because they lead to and are combined with further modi- 

 fications which change such lizards in Oaxaca and on the Isthmus 

 into a form to which the name of communis is no longer 

 applicable. 



Of the specimens described in the accompanying table (p. 348), 

 only those from Colima, Manzanillo, San Domingo de Guzman, 

 and appai'ently those from the island of Cozumel, conform with 

 G. communis copei. Possibly those mentioned by Cope from 

 Guatemala may exhibit the same characters, especially the 

 forearm scutes. 



Cope's types, about 40 specimens, were sent to Washington by 

 Xantus, wlio had collected them in the State of Colima, Western 

 Mexico. In the original description, Trans. Am. Phil. Soc. 1877, 

 p. 95, it is stated that G. communis has a frenocular, large post- 



