306 I)R. H. GADOW ON EVOLUIIOX [Mar. 20, 



Femoral pores less than 18. 



Collar composed of large scales (see above). 



No pale field-spots. 



6 white stripes and a mid-field with 1 oi' 2 pale stripes. 



Male with white under parts. 

 It will be found from examination of the tabular statistics of 

 C. deiypei, of. p. 315, that such C. deppei actually occur in the 

 lowlands of South Guerrero, notably between the coast and San 

 Luis Allende. Specimens from other countries are ruled out of 

 comparison eithe)- by their numerous stripes or femoral j^oi-es, &c. 

 There is in particular one of the specimens from Oocoyul (text- 

 fig. 73 C and text-fig. 65 E) which should be a fair test case. It 

 happens to be a young male of 63 mm., and the only obvious 

 difleiences from C. sexlineotus of Sauz (text-fig. 73 A, B) are the 

 sharply marked black of the collai-, and that the 4th supraocular 

 is represented by a tiny remnant only. Since it is in this district 

 of Guerrei'o that the 4th supraocular crops up not unfi-equently, 

 females, without the criterion of the l>lack undei- parts, may easily 

 appear undistinguishable from typical C. sexlineatus. 



I consider this an example of extraoi'dinary convei-gence of two 

 perfectly "good species" which nowhere are known to commingle. 

 Specimens of one clan of the northern species, in the very north 

 of Mexico, and specimens of one clan of the tropical, southern 

 species in South Guerrero, have hit upon the same combination of 

 numerous characters so as to have become practically not dis- 

 tinguishable ! There is scarcely a greater diftei'ence in physical 

 features imaginable than between the wind-swept, droughty arid 

 plateau of Sauz and the hilly woody lowlands of tropical Gueri-ero. 

 It is inconceivable that members of the same species of Cnemi- 

 dophorus (lizards which so obviously react upon the physical 

 featui'es of their surroundings) should vary in exactly the same 

 direction in such absolutely different places. On the contrary, we 

 must conclude that the two clans are of different sjjecies ; in 

 other words, that these Sauz and Guerrero specimeiis are an 

 illustration of convergence. 



At the same time, Avithout attempting to quibble, we may 

 consider it fairly proved that C. sexUneatus and C. deppei are very 

 closely related to each other, so intimately that they might be 

 considered as the two divergent races of one species, upon the 

 ground that, taken in a lump, they have now been shown to 

 " run into each other." Only, there are these grave diflicidties. 

 Fii'st, they do not live together but are hopelessly separated. 

 Secondly, G. sexlineatus forms the starting-point for species like 

 G. gularis with strongly enlarged forearm- scales and a stiong 

 collar, while the tendencies of C. deppei are the increasing number 

 of stripes, black pigmentation of the males' underparts, and loss of 

 the 4th supiaocular. Lastly, from some form like G. deppei have 

 been developed G. immutahilis and G. gutiaius, lizards wdiich have 

 radiated in a direction opposite to that of the " descendants " of 

 G. sexlineatus. 



