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Show 354 DR. H. GADOW ON EVOLUTION [Mar. 20, Southern Railway, about 70 miles N.W. of the town of Oaxaca, and situated almost at the bottom of the deep depression in which collect the head-waters of the River Papaloapan, which mighty river empties itself into the lagoons near Alvarado, south of Vera Cruz, The bottom of the depression is only 600 metres, about 1900 feet, above sea-level, and a rather steep ascent leads to the plateau of the Valley of Oaxaca, 1600 m. = 5250 feet, with an intervening ridge of still greater height. Towards the north-west the ascent out of the gorge is more gradual, but it reaches, before Puebla, an altitude of nearly 8000 feet. To the west is a succession of high mountains. The climate in this long depression is very hot, thoroughly tropical, but of the dry type, as shown by the prevalence of Organ-cactus, small Mimosas, and scrubby Acacias, with scanty low vegetation on the red, gravelly rubble which forms the subsoil. W e are still in complete zoological ignorance about the country for at least 120 miles all around Cuicatlan, except the neighbourhood of the town of Oaxaca. There occur only G. mexicanus and C. bocourti; to the east of the depression are dense mountain-forests, in which lower down lives only C. guttatus with Ameiva; at Puebla lives C. communis occidentalis, which in its striking pattern, but not structurally, bears a great resemblance to the Cuicatlan specimens. Supraoculars always 4, followed behind b)T many small granules, especially when (3 specimens) the posterior supraocular is extremely small, almost reduced to the vanishing point. Frenocular present in 11 specimens; two specimens have a frenocular on the right side only ; in the 12th, a young specimen, the frenocular of both sides is fused with the first preocular. Collar (text-figs. 64 C, 65 F) composed of mostly medium-sized to rather small scales, sometimes passing quite gradually into the gulars. In nearly nil specimens at least some granules are visible between the scales of the posterior border, and sometimes these granules form a, complete row. But in the largest specimen, and in one of 72 mm., the scales forming the edge are distinctly large. Humerus covered in front with many rows of scales, about 8 to 10 in all; sometimes they decrease in size from before backwards, and as a rule the hindmost rows are continuous with the slightly enlarged granules of the forearm ; but in most cases some of the front rows, either 2, mostly 3, rarely 5 or ('», are distinctly larger than the rest. Forearm covered in front with 2|, mostly 3, complete rows of scutes. Forearm, posterior surface, never covered with scutes or scales. In 5 specimens the granules are almost imperceptibly larger than the rest; in 5 other specimens are several rows of slightly enlarged granules, either near the elbow or near the wrist; only in 2 specimens enlarged polygonal granules form three long rows. Femur.-The rows of scales show a continuous variation from 6 to 9. 6 occurred 3 times ; 6 to 7 irregular twice; 6 right. |