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Show 1897.] LIZARDS OP THE GENUS SCELOPORUS. 493 Males are usually distinguished from females by the presence of blue on the throat and on the sides of the belly; but this character should not be exclusively relied upon for distinguishing the sexes, since a female from Presidio has the throat as blue as some males collected at the same time in the same locality; whilst, on the other hand, an adult male specimen of the var. horrldus from Puentillo de Acatan entirely agrees with normal females in the coloration of the lower surfaces. The intensity of the blue varies much, probably according to seasons. The male of the typical S. spinosus is described as wdth a blue throat striped with darker, the sides of the belly blue, the breast and the middle line of the belly white ; a large black blotch in front of the arm : such specimens we possess from Guanajuato, Puebla, and Presidio (/'. typlca) and from Ixtlan (var. horrldus). In S. horrldus the blue of the belly may extend on the anterior face of the thigh, as in our specimen from N. of Eio de Santiago, and in one from Mexico referred by m e to the var. clarkil. The type of S. clarkil is described as with " a bluish abdomen, indistinctly black along the middle region ; the lower surface of the head is blue, on the middle region surrounded with black." This description might have been penned from one of our specimens from Presidio, near Mazatlan, and agrees well with the male from Port Lowell which I regard as a typical S. clarkil. Hallowell's S. magister has " two large bluish-green blotches upon the abdomen, one on each side, and one upon the neck; the rest of the under surface light straw-yellow." Specimens answering to this description I have only seen from Mexico (/• typlca). Specimens from Arizona, referred to S. magister, have the throat blue posteriorly, with a black cross-band, and the sides of the belly of a deep blue edged with black within ; groin black. Specimens (not full-grown) from Texas and Tampico have the sides of the belly greenish blue and a small spot of the same colour on each side of the throat. The systematic treatment of the Sceloporl here grouped under S. spinosus is a subject on which recent authors have shown great divergence of opinion. In his Synopsis of 1885, Cope attaches undue importance to the number of femoral pores, a character which he regards as " not subject to such variations as to be embarrassing;" and he forthwith makes a bold primary division into species with 2-6 pores and with 10 and more. The S. horrldus (wdth 2-6 pores) is therefore placed quite apart from S. spinosus (believed to have 10 or more). This shows that the author cannot have counted the pores in a very large number of specimens, for the series in the British Museum alone, which I daresay is far less important in numbers than that to which he had access, contains not only specimens with 7, 8, or 9 pores, which therefore would not fit in either division of the synopsis, but there is even a specimen, from Guanajuato, with 7 pores on one side and 10 on the other. S. clarkil, usually accepted as a distinct species, or subspecies, by Cope and other American authors, is not even mentioned in this synopsis. Z O O L . Soc.-1897, N o , X X X I I I . 33 |