312 DR. H. GADOW OX EVOLUTIOX [Mar. 20, 



The amplitude of variation I have found, in 100 specimens, to 

 extend from 14 to 22, but the solitary case- of 14 was quite ex- 

 ceptional, it being associated with 16 on the other leg; and 22 

 likewise occurred once only, being coupled with 21 on the other 

 side. 15/15 occurred twice, 15/16 twice, 16/16 four times, 21/21 

 only two or three times. The usual numbei's are 17 and 18. 



The specimens fi-om Tierra Coloi-ada possess the highest number, 

 average mean 18"8 ; those of the Pacific side of Guerrero have 

 the smallest number, average 16*2, and this smallest number 

 coincides with the lowest number of femoral scales. The Balsas 

 specimens take up a middle position, with 17'5 as their mean. 



The apyjended table refers only to such localities in which 

 sufficient material was collected. It also shows that the right 

 and left sides are practically equal. 



Total number of Pores. 



Tequesixtlan. | Eidit 333 



18 specimens. ) 

 Tievra Colorada | .04. 



23 specimens, j " 



Rio Balsas. \ ..^^ 



25 specimens. ) " 



Coast to S. Luis. ) „„, 



19 specimens. ) " 



Left 337 



Mean 



18-6 Pores. 



„ 429 



„ 



18-8 „ 



» 437 



„ 



17-0 „ 



„ 311 





16-2 „ 



1533 1514 17 or 18 



Length of Mud Urnh. — The claw of the fourth toe usually 

 reaches the ear, but sometimes it falls a little short of it. 



Throat (text-fig. 65 C, E). — Some of the granidar scales covering 

 the upper half of the throat are, as a rule, slightly larger in the 

 centre than nearer the sides ; occasionally they ai-e large enough 

 to form an ill-defined little cluster, which, however, is rarely so 

 conspicuous as it is in many specimens of C. immutab'dis (text- 

 fig. 65 A). 



The Collar (text-fig. 65 C, E) varies much in composition. In 

 the majority, one or more rows of the lai-ge scales extend right 

 across, while in C. immutahilis the large scales are mostly con- 

 fined to the middle third, becoming considerably smaller towards 

 the sides. The presence or absence of tiny granules on the 

 posterior border of the collar is no criterion whatever in any 

 species of Cnemidojyhorus. They are either absent, or here and 

 tliei'e one is intercalated between the scales, or they form a single, 

 or even several complete rows of granules. Lastly, it is to be 

 noted that this character is often due solely to the shrinking of 

 the soft granular fold in spirit-sy^ecimens. 



Coloration (text-fig. 66; text-figs. 71 k. 72). — The variations in 

 colour and pattern extend fai- lieyond the limits which I was able 

 to describe in my first paper. The range of white or pale longi- 

 tudinal stripes extends from 6 to 11 ; and the whole of the 

 under parts, from the jaws to the anal i-egion, varies in adidt 

 from uniformly silver-white to deep black. It is important to 



