338 DR. n. GADow ON EVOLUTION [Mar. 20, 



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

 follow, towards the throat, several shorter rows of scales which 

 decrease in size. Posterior sm-face of forearm with at least some 

 large scutes. Fi-enoculai- variable. The young start with from 

 6 to 8 whitish stripes, which become dull, whilst tvhite sjmts develop 

 vnthin 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 gi'ound in about 10 longi- 

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

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

 often pink. Chest and abdomen are eai-ly sufi'used with blue ; 

 with advancing age chequered blue and black, with whitish edges 

 to the scales. 



Cope was quite justified in separating Mexican Cnemidophori 

 of lai-ger size, with essential gidaris sti-ucture (4 supraoculars, 

 strong collar, and lai'ge forearm scutes), and in which the stripes 

 bi-eak up into rows of spots, as C. gidaris communis ; but he did 

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

 insufficient Mexican material. 



The diagnosis or description given above suits the majority of 

 those Ciiemidojihori which ai'e known fi'om 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 aci'oss the plateau from, roughly speaking, Guadalajara, to 

 Guanajuato and Paebla. But in this wide stretch of varied 

 country they exhibit considerable changes, — changes which at 

 first crop up as unimportant, individual variations, but wdiich 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 Miehoacan the stripes are moi'e persistent 

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

 reduced to granules. In Colima, the pores and the I'ows 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 TehuanteiDec 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. gularis, whilst they could well figure as 

 a race of C. communis. At the same time, they appi'oach the less 

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

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



Further, in the basin of the Balsas Kiver C. communis is 

 represented by a form which is striicturally an intensified 

 C. gidaris, and removed as far as po;-sible from the southei'n 

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

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

 further east, in Oaxaca, the old specimens are tiger-barred with 

 a variable, partly granidar collar and with smaller and fewer 

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



