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Show 346 DR. H. GAD0W ON EVOLUTION [Mar. 20, munis and lead on to the Puebla clan, in which the characters of C. communis are again intensified. There is still a gap between San Juan del Rio and Puebla, a distance of 150 miles, whence no Cnemidophori have been recorded. I myself have never seen a single specimen in the Valley of Mexico, an absence due no doubt to the high elevation, 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 3U0 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 Cnemidophorus. 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 certain 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 rather likely that the spotted clan at Puebla, with its isolation from the other C. communis, represents a cr.se of convergent evolution. G. c. balsas itself is a case of isolation; they are restricted 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 south by the Sierra Madre del Sur, the low pass 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 Cnemidophori in Western Michoacan, whether they change or not, into the western form, remains for the present unknown. The same applies to the zoologically undiscovered wide districts of the upper basin of the Balsas. CNEMIDOPHORUS COMMUNIS COFEI. (Text-figs. 78 A, C, E.) Differing from C. communis occidentalis by the increased number of humeral and femoral rows, greater number of pores, and larger size of the body. Although these are differences of degree only, they are significant because they lead to and are combined with further modifications which change such lizards in Oaxaca and on the Isthmus into a form to which the name of communis is no longer applicable.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 apparently 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, who had collected them in the State of Colima, Western Mexico. In the original description, Trans. A m . Phil. Soc. 1877, p. 95, it is stated that C. communis has a frenocular, large post- |