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Show 1906.] IN MEXICAN LIZARDS. 287 species, subspecies, races and varieties, I have proceeded to point out those individuals which upset the diagnoses. Cope has rightly said, Report U.S. Nat. Mus. for 1898 (1900) p. 569 :-" The discrimination of the North American species of this genus is the most difficult problem in our herpetology. Nowhere are subspecies more sharply defined than in Cnemidophorus, that is geographical forms, which are not always true to their characters." He, however, practically left the Mexicans untouched, confining himself to those of the United States. Most of the " species " are so plastic, so variable, that they may well drive the systematist to despair. Not two authorities will, nor can, possibly agree upon the number of admissible species. The Cnemidophori in their unsettled condition, are truly delightful as an ideal object lesson in Nature's way of species-making. It has been m y ambition to find truly intermediate individuals, real links between the groups and between the reasonably supposed species. This was suprisingly difficult! It was a reasonable premiss that such links should occur at the same place, at least in the same district, with the two forms to be linked. If the link occurs somewhere else, the question enters a new field of inquiry. It is fairly certain that the three forms of the dej^pei-group, C. deppei, C. immutabilis, and C. guttatus, are closely allied to each other; and it may now be taken as proven that C. immutabilis turns into G. guttatus in consequence of living in the Atlantic Tierra caliente. These two forms actually run into each other, but they are easily separable when in their respective typical garbs, in which case, moreover, slight structural differences are apparent. Result: C. guttatus is a terminus of evolution, as being the spotted race of C. immutabilis-scientifically expressed, C. immutabilis, var. guttata; but thanks to accident, priority of naming, it has to stand as C guttatus guttatus, and the parental stock form stands as C. guttatus, var. immutabilis ! No sense in that, but justice is done to the fetish, although not to the lizards to which these paraphernalia should be subservient. Further, the Salina Cruz, Tequesixtlan, &c, specimens of Oaxaca are typical, intensified C. immutabilis ; they can hold no intercourse with those of the Atlantic side, a point about which I am positive, owing to the configuration of the country Mingling still occurs on the isthmus proper; and in the forest-lands of Guerrero C. immutabilis tends to assume the spotted garb N o w let us assume that these woods were destroyed for ever and that the divide between the Atlantic and Pacific hot-lands is also laid bare, then we should have the typical C. guttatus in the Atlantic Tierra caliente, and the typical C. immutabilis on the Pacific coast: two good species, because they are weJl defined and geographically separated. They were considered as good species by Cope and by Boulenger; but I found the intermediate forms in districts of intermediate bionomic conditions, so that now at |