1906.] 



IN MEXICAN LIZARDS. 



283 



oblique to their main axis. Cope and others have employed the 

 relative length of the hind limb as expressed by the point which 

 the longest adpressed toe reaches on the neck, ear, or eye. This 

 criterion had to be discarded on account of astonishing variation 

 in allied individuals. 



Text-fio-. 64. 



Lepiilosis of the collar and throat. 



A=C. tessellatus from El Paso, Field Colurab. Mus. Collar composed entirely 



of small, mostly granular scales. 

 B = 0. mexicanus, from Totolapan No. 2. 

 C=0. communis austral is, Cuicathin, 140 mm. 

 D=C. communis australis, Laguna. Collar composed entirely of large scales. 



The skin of the back is granular, but the grains may be fine or 

 coarse ; there is no way of expressing this intelligibly ; moreover, 

 counting of the grains across the middle of the body reveals 

 enormous individual differences — for instance, in 0. guttatus of 

 Aqvia fria from 100-180 granules across. 



The arrangement of the scaling of the preanal region proved 

 likewise unmanageable. It does not follow that these discarded 

 characters ai-e of no systematic value. On the conti-aiy, the svim 



