1906.] 



I.NT MEXICAX LIZARDS. 



293 



voiighly speaking within a triangle from Tampieo and Vera Cruz 

 to Zacatecas. Most of the latter State lies too iiigh ; and this 

 altitude would be a sufficient factor for stopping the eastward 

 extension of C. communis and its allies. No Cnemidophori have 

 ever been recorded from Jalapa, although that district has been 

 the hunting-ground of many good collectors ; none are known 

 from Orizaba district, and the Comision cientifica (c/. Cope's List, 

 Proc. Am. Phil. Soc. 1885, p. 372) returned none from the State 

 of Hidalgo. The northern half of the State of Vera Cruz is 

 covered mostly with rain- forest. The reputed absence in the 

 triangle is easiest accounted for by the assumption that C. gularis 

 coming from the North, and C. depiiei with C. guttatus from the 

 South, have not yet met, perhaps cainiot meet on account of 

 unsuitable bionomic conditions. 



12 3 3 



I 2 3 



Text-fig. 70. 



12 3 3 



12 3 3 





Evolution of Pattern of C. tessellatus A-D and of C. ruhklus E. 



How, then, have we to imagine that the spreading of Cnemido- 

 phorus in Mexico has taken place ? Of course we leave aside the 

 idea of a multiple origin. The usual explanation of zoogeographers 

 would be as follows : — Some indifferent species spi-eading from the 

 South through the Pacific half of the country northwards, and 

 thence into the United States, has on its way given rise to the 

 various forms of lizards. This not unreasonable assumption, if 

 «,pplied to the species as we actually find them distributed, Avould 

 imply that they have changed, say, from A into B into . . . E, each 

 with side-branches or sub-species, but that on their arrival in the 

 North in the form U they have been turned again into something 

 like A. Dejypei and sexlineatas axe near allies, but such a 

 i-eversion or return to pristine conditions is most unlikely. It 

 would, moreover, mean that E, while assuming ^-l-like characters, 

 must also be rather like B. But in reality this is not the case. 

 On the contrary, A [sexlineatus) tui-ns into E (gidat^is) ; this in 

 turn into J) and C (commttnis occidentcdis) ; C into B {C. cojjei), 

 the var. austrcdis of which we have some occasional difficulty in 



20* 



