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



and two neighboui-ing spots in each field become confluent 

 transversely, and this process, accompanied by active encroach- 

 ment of the dark field-pigment upon the stripes (themselves fading 

 away, or breaking up), may lead to a marbled, pai-tly cross-barred, 

 or completely tiger-baii'ed transverse pattern. Lastly, a partly 

 monochi'ome condition may gradually asseit itself with advancing 

 age, proceeding from the neck towards the back, or from the i-ump 

 forwai-ds, but with black spots upon the lighter gi-ound-colour. 

 Oi' the monochrome tendency proceeds from the neck backwards, 

 and in this case the ground-colour is dai-k with pale spots. 



Key to the S'pecies d-c. of the GVLAms-Growp. 

 (Text-figs. 68 & 69.) 



Small, less than Stripes and pale field-spots persistent. 



80 mm. North Mexico, Arizona, and Texas, gularis. 



Large, 100 mm. Stripes broken by the encroaching black of 

 and more. the iields. 



Stripes broken on lower back. Few field- 

 spots California. septemviUatus. 



Stripes completelj' broken bj' the field black 

 and by the transverselj' combining 

 field-spots. Resulting in tiger-barred 



pattern South Mexico, mexicanus. 



Stripes dissolved into rows of pale spots. 

 Fields with rows of spots. 

 Resulting in narrowly cross-barred j'ellow- 



and-black pattern Chihuahua, scidaris. 



Resulting in many longitudinal rows of pale 



and round spots Mexico, communis. 



Forearm with scutes or jjolygones. 

 5-7 humeral and femoral rows. 



Chest and abdomen pale var. occidentalis. 



„ „ blue-black \-Av.bocourti. 



8-9 humerals and f emorals var. cope't. 



Forearm entirelj' granular \&v. aiistralis. 



Stripes vanishing or cut up except the second. 

 No field-spots. Collar black in adult. 



Tres Mai'ias Islands, mariarum. 

 Uniformly olive, with 6 rows of black spots. 



Texas, Coahuila. semifasciattis. 



Cnemidophorus mariarum Giinther. 



Five specimens collected by Forrer on the Tres Maiias Islands : 

 3 very young, one immature, one adult of 121 mm, 



Sitpraorhltals 4. 



Collar composed of rather weak scales, but of the type of the 

 (jularis-^vox\\t ; without granules on the posterior edge. There is 

 a perceptible nest of somewhat larger granules on the throat. 



Ilmnerits with about 5 rows of larger scales, followed by a few 

 of much smaller size. 



Posterior side of forearm with a very large I'ow of scutes, besides 

 smaller scutes. 



Femur covered with 7, 8 and 8 to 9 rows of scales, counting 

 from the largest row to the pores ; but there are several rows 

 beyond the largest row, as is often the case in Cnemidophorus, and 



