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Show 328 DR. n. G A D O W O N EVOLUTION [Mar. 20, and two neighbouring spots in each field become confluent transversely, and this process, accompanied by active encroachment of the dark field-pigment upon the stripes (themselves fading away, or breaking up), may lead to a marbled, partly cross-barred, or completely tiger-barred transverse pattern. Lastly, a partly monochrome condition may gradually assert itself with advancing age, proceeding from the neck towards the back, or from the rump forwards, but with black spots upon the lighter ground-colour. Or the monochrome tendency proceeds from the neck backwards, and in this case the ground-colour is dark with pale spots. Key to the Species &c. of the GULARis-Group. (Text-figs. 68 & 69.) Small, less than Stripes and pale field-spots persistent. 80 m m . North Mexico, Arizona, and Texas, gularis. Large, 100 m m . Stripes broken by the encroaching black of and more. the fields. Stripes broken on lower back. Few field-spots California, septemvittatus. Stripes completely broken by the field black and by the transversel}' combining field-spots. Resulting in tiger-barred pattern South Mexico, mexicanus. Stripes dissolved into rows of pale spots. Fields with rows of spots. Kesulting in narrowly cross-barred yellow-and- black pattern Chihuahua, scalaris. Resulting in many longitudinal rows of pale and round spots Mexico, communis. Forearm with scutes or polygones. 5-7 humeral and femoral rows. Chest and abdomen pale var. occidentalis. „ „ blue-black var. bocourti. 8-9 humerals and femorals var. copei. Forearm entirely granular var. a ustralis. Stripes vanishing or cut up except the second. N o field-spots. Collar black in adult. Tres Marias Islands, mariarum. Uniformly olive, with 6 rows of black spots. Texas, Coahuila. semifasciatus. CNEMIDOPHORUS MARIARUM Giinther. Five specimens collected by Forrer on the Tres Marias Islands 3 very young, one immature, one adult of 121 mm. Supraorbitals 4. Collar composed of rather weak scales, but of the type of the gularis-group ; without granules on the posterior edge. There is a perceptible nest of somewhat larger granules on the throat. Humerus with about 5 rows of larger scales, followed by a few of much smaller size. Posterior side of forearm with a very large row of scutes, besides smaller scutes. Femur covered with 7, 8 and 8 to 9 rows of scales, counting from the largest row to the pores ; but there are several rows beyond the largest row, as is often the case in Cnemidophorus, and |