1906. 



I.NT MEXICAN LIZARDS. 



293 



roughly speaking within a triangle from Tanipico and Yera 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 Gnemidophori have 

 ever been recorded from Jakpa, 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. gidaris 

 ■coming from the Korth, and C. deppei with G. guUatus from the 

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

 unsuitable bionomic conditions. 



Text-fio-. 70. 



12 3 3 12 3 3 



2 3 3 



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



How, then, have we to imagine that the sjoreading of Gnemido- 

 pliorus 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 spreading 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 

 -applied to the species as we actually find them distributed, would 

 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 E they have been turned again into something 

 like A. Deppei and sexlineatas are near allies, but such a 

 reversion or return to pristine conditions is most unlikely. It 

 would, moreover, mean that E, while assuming ^4 -like characters, 

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

 On the contrary, A (sexlineatus) turns into E [gidaris) ; this in 

 turn into I) and G {commimiis occidentcdis) ; G into B {G. eopei), 

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



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