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Show 358 DR. H. GADOW O N EVOLUTION [Mar. 20, opposite to C. guttatus and to those specimens of G communis copei and C. c. australis from Colima, the Isthmus*, and Cuicatlan, which are very similarly coloured. In fact (7. toowtf is structurally indistinguishable from many specimens of C. communis occidentalis, and from some ot the C. mexicanus of the Balsas basin. Fundamentally, the evolution of its pattern is that of the former, but when most agreeing in coloration with the copei or australis varieties it differs most from these structurally; or, vice versa, when structurally most like mexicanus it is diametrically opposed to it in coloration. Upon this ambiguity rests the best claim for separate recognition of G. bocourti, which after all happens to be one of the most easily recognised forms of the whole C. gularis group. CNEMIDOPHORUS MEXICANUS Peters. (Text-figs. 69; 81 A, B, C, D, F; 82 A - D , &c.) Diagnosis.-Large-sized C. gularis in which the original stripes do not develop pale spots, but are broken up by the encroaching black of the fields and by the transversely combining brownish field-spots, resulting eventually in a tiger-barred pattern. The most extreme development is reached in Oaxaca; this variety I distinguish as var. typica. They reach the largest size, the tiger-pattern is most pronounced, but the collar and the covering of the posterior side of the forearm are variable, inclining more towards granules. Those of the Balsas River-basin are distinguished by a strong collar, prevalence of scutes on the forearm, and far less pronounced, more incipient tiger-pattern. They seem, moreover, as fits their distribution, to pass into aberrant C. communis occidentalis. These I refer to as G. mexicanus var. balsas. It is significant that these Oaxaca specimens exhibit the same trend of variation away from their relations (decreasing collar and more granular arm-scales and tendency to tiger-pattern) as do the representatives of C. communis copei in the State of Oaxaca in the shape of C. c. australis. It is irony of fate that the three type-specimens of C. mexicanus are all immature, and show but little of the typical features. Range,-The temperate regions of the States of Oaxaca and Guerrero, descending into the tropics of South Oaxaca and into the tropical portion of the Balsas basin. Supraoculars 4, apparently without exception; the posterior separated from the parietal plates by one row of three or four elongated granules. Frenocular variable. Collar variable. It reaches its largest development in the var. balsas, being composed of very large scales, one row of which * In my paper Proc. R. S. 1903, p. 118, I had referred to C. bocourti the large specimen from San Domingo, now mentioned as C. communis copei, p. 350; and the Nayarete specimens now described on p. 342. |