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Show 368 DR. H. GAD0W ON EVOLUTION [Mar. 20, Key to the Species dx. of the TESSELLATVS-Group. Nasal not touching second labial. Throat pale, not spotted. 7 stripes, no field-spots. Length 86 m m . New Mexico. C. perplc.rus. 8 stripes, no field-spots. Length 60 m m . Nuevo Leon. C. octolineatus. N o stripes, no field-spots. Length 56 m m . Nuevo Leon. C. inornatus. Throat pale, with dark spots. Brown marbled. Length 120 m m . Lower California. C. maximus. With field-spots and stripes, ultimately spotted and barred with black and white. Length . Q tesseUatu^ 102 m m South-western U.8.A. < =stejneaeri Becomes unicoloured, with 3 rows of blackish *• ' J •" spots. Thighs and tail below vermilion. Length 100 m m . San Margarita Island, West Lower California. C. rubidus. Throat and rest of under parts blackish. Vermiculated and spotted on bluish ground. . Q mehmosMhus. Length 86 m m . North Mexico to Arizona. < __r, . 7 Monochrome blackish. Length 82 m m . <- _ u ' variolosus- Sonora and San Martyr Island, Gulf ( n . . of California j ^CathiTs Nasal in contact with second labial. *• ' a n0Ps- Only 12 or 13 pores. Length 55 m m . Cedros Island, Lower California. C. labialis. TESSELLA res-Group. Definition.-Cnemidophorus with 4 supraoculars, a collar composed of many small scales, and the posterior side of the forearm covered with granules only. This group, centred in Sonoraland, is composed of a great number of definable forms and has a very wide distribution; roughly speaking, from San Francisco across Nevada to the Great Salt Lake, thence south-eastwards through the whole basin of the Rio Grande down to Laredo, from El Paso to Hermosillo in Sonora, and from the southern end of Lower California again to San Francisco. Nearly the whole of this wide range is inhabited by the central form C. tessellatus with its correspondingly greatest amount of variation in structure and pattern of coloration. Almost all the other forms are rather local. CNEMIDOPHORUS PERPLEXUS Baird. Unfortunately only two specimens of this apparently least specialised kind could be examined. Some have been recorded from the Valley of the Rio Grande near and north of El Paso; others from Pecos in Texas by A. E. Brown, Proc. Acad. Phil. 1903, p. 547. According to Cope, the colour-characters are the possession and retention of 7 stripes, absence of pale spots in the fields, and absence of dark spots on the throat and on the rest of the under parts. Larger humeral scales in 4 rows, femorals in 6 rows, counting from the largest to the pores which number 19 ; size from snout to vent 86 m m. |