1906.] IN MEXICAN LIZARDS. 337 



Forearm, posterior surface, always covered with much-enlarged 

 scutes, the largest in the middle, reaching towards the wrist ; on 

 the elbow continuous with the 6th or 5th, rarely with the 4th 

 row of humeral scales. 



Femur : Mostly with 5 very regular rows, rarely with 6, which 

 are then rather irregularly disposed ; the three largest rows reach 

 the knee as in C. dejijiei. One specimen, 60 mm., has 7 unmis- 

 takable rows ; another of 50 mm. has 7 incomplete right and 

 6 regulai' rows on the left thigh. 



Tibia covered with 2 very large rows, with a third smaller row 

 on the fibular side, i. e. the side turned towards the taiL 



Preancd isihmus short, with only one or two ti^ansverse I'ows 

 of small scales between the ventrals and the preanal plates. 

 The detail is very variable. 



Femoral pores: Fi'om 15/17 once, to 21/21 once. Usually 

 with 17, 18, or 19 rows; 20 did not occur. The solitary occur- 

 rence of 21/21 refers to a specimen 60 mm. in length ; the only 

 one possessing 7 femoral rows of scales, and further distinguished 

 by the almost complete absence of pale spots in the black dorsal 

 fields. 



Coloration and pattern. — Under parts of young white and 

 mother-of-pearl ; immature specimens have the chest and abdomen 

 suffused with pale bluish, and dark pigment appears in the basal 

 portion of the scales. In the adult, throat, collar, thighs, and 

 tail are yellowish white ; chest and flanks, less so the belly, are 

 mottled blue-black, the edges of the scales remaining whitish. 



Upper surface (figs. 68 & 76). The young start with 6 sharp 

 white stripes, with single or double rows of pale spots in the 

 fields, and also with a row of white spots in the middle line. 

 In specimens of about 70 mm. the stripes have become diUl to 

 pale grey, with small white dots in the dulled stripes. Field-spots 

 brown, yellow, or brown-yellow, and more numerous, and their 

 double rows in each field become confluent. Ultimately the stripes 

 are lost, remaining traceable longest on the neck ; the whole back 

 is covered with numerous cross-bars or vermiculations of deep 

 black and vivid yellow, or orange, with many white spots on the 

 thighs, legs, and rump. In some beautiful specimens the tiger- 

 bar pattern is complete, there being about 30 black cross-bars 

 from nape to tail ; whilst the back approaches the cross-bar stage, 

 the white stripe on the hinder sui-face of the thigh is dissolved 

 into irregular white spots. 



C. scalaris is known only from near Chihuahua town, and 

 plateau to the south of it, excejjt two specimens "from Arizona" 

 according to Cope. 



According to the evolution of the pattern from 3'outh to adult 

 age (for instance, the very pronounced white spots in the stripes), 

 this lizard is closely allied to C. communis. 



Onemidophorus communis Cope. 

 Diagnosis. — 4 supraoculars. Collar sti^ong, composed of at least 



