338 DR. H. GADOW OX EvoLUTiox [Mar. 20, 



one complete row of large scales which form the edge ; upon this 

 follow, towards the throat, several shoi'ter rows of scales which 

 decrease in size. Posterior surface of forearm with at least some 

 ■ large scutes. Frenocular variable. The young start with from 

 6 to 8 whitish stt^ipes, lohich become dull, lohilst lohite sjjots develop 

 uiithin most of these stripes. Fields at first dark, later on light 

 spots develop in them, mostly rounded and well-defined. Ultimate 

 residt: many spots on very dark ground in about 10 longi- 

 tudinal rows, and numerous small whitish spots on the rump, 

 root of tail, and on the thighs. Throat and collar light-coloured, 

 often pink. Chest and abdomen are early sufli'used with bkie ; 

 with advancing age chequered blue and black, with whitish edges 

 to the scales. 



Cope was quite justified in separating Mexican Cnemidophori 

 of larger size, with essential gidaris structure (4 supraoculars, 

 strong collar, and large forearm scutes), and in which the stripes 

 break up into rows of spots, as C. gidaris communis ; but he did 

 not know, or he ignored, C. bocourti, and he had only a very 

 insuificient Mexican material. 



The diagnosis or description given above suits the majority of 

 those Cnemido2)hori which are known from the western half of 

 the Mexican plateau and its western and south-western slopes, 

 from the north-west of Chihuahua to Colima and Manzanillo ; 

 and across the plateau from, roughly speaking, Guadalajara, to 

 Guanajuato and Puebla. But in this wide stretch of varied 

 country they exhibit considerable changes, — changes which at 

 first crop uj) as unimportant, individual variations, but which in 

 neighbouring districts have become the rule ; and to these are 

 added changes of other characters, until their combination com- 

 pletely upsets the original diagnosis. 



Thus, for instance, in Michoacan the stripes are more persistent 

 and the scutes of the forearm are more polygonal, smaller, even 

 reduced to granules. In Colima, the pores and the rows of 

 scales on the humerus and femur are distinctly more numerous. 

 At Manzanillo, these changes are combined with smaller collar- 

 scales ; while on the Isthmus of Tehviantepec and in Oaxaca, at 

 Cuicatlan, an entirely granular forearm is added; so that nothing 

 is left which could justify us to enumerate these specimens as a 

 subspecies or a race of C. gidaris, whilst they could well figure as 

 a race of C. communis. At the same time, they approach the less 

 typical specimens of C. immutabilis and C. guttatus to such an 

 extent, that it is not always easy to keep them asunder. 



Fui-ther, in the basin of the Balsas River C communis is 

 represented by a foi'm which is structurally an intensified 

 C: gidaris, and removed as far as possible from the southern 

 variations, but the spotty character is gone, and the tendency to 

 destroy the stripes by cross-bars begins to assert itself, until 

 fui'ther east, in Oaxaca, the old specimens are tiger-barred with 

 a variable, pai'tly granular collar and with smaller and fewer 

 scutes on the forearm. These are C mexicanus, which may well 



