TEIID LIZARDS OF THE GENUS CNEMIDOrHORUS 143 



Hahitat and hahlts. — Nothing!: is known concerninj^ the lial)itat 

 and habits of this lizard. Mr. Slevin has informed the writer that 

 he has made strenuous attempts to collect this interesting and rare 

 species on Cerros Island during his more recent collecting expedi- 

 tions to Lower California, but that he has always failed. 



Affinities. — The definition of the affinities of tliis species is difficult. 

 Gadow (190G) was much puzzled over the relationships and wrote 

 as follows : " The arrangements of the labials and nasals is unique. 

 The condition of the collar is essentially that of the tessellatas group, 

 but recalling the gvJans group by its sharp edge without granules. 

 However a very similar collar is given to octolineatus and inornatus 

 in Cope's figures. The slightly enlarged granules on the forearm 

 l)oint to depjni and sexliiieatus to which latter it is more closely 

 related by the color pattern. The three peculiar pale stripes on the 

 hind limb recall tlie three equally peculiar stripes of mart yi -is.'''' 



Because of its geographical position and characters, particidai'ily 

 the possession of tw^o frontoparietal plates, lahialis is here regarded 

 as a member of the sexlineatus group. The retention of the striped 

 condition throughout life is characteristic of the entire hyperythi'-us 

 group, and its appearance in lahkdis would be more significant if it 

 were not also entirely characteristic of sexlineatus itself. 



The irregular placing of the longitudinal caudal keels and the low 

 luimber of femoral pores found in lahialis show as much variation 

 from typical hyperythrus as from typical perplexii,^., so these charac- 

 ters give no clue to the origin of the form. However, for reasons to 

 be given in the general discussion at the end of this work (pp. 251-260) , 

 the hyperythnis group is presumed to have been derived from the sex- 

 lineatus group through a conunon ancestral stock with pefplexus. 

 The same transient stock that produced hyperythnis apparently gave 

 rise to lahialis^ too, the latter becoming differentiated before the union 

 of the frontoparietal elements, the former differentiating later by 

 such change. Even today lahialis is largely intermediate between 

 hyperythnis and perplexus^ for the retention of a high number of 

 dorsal stripes and the lack of differentiation between the dorsolateral 

 (uppei- or third pair) and lateral stripes suggest pcrplexiis, while on 

 tlie other hand, the small size of the l>()dy in adults and the frequent 

 foi'king of the middorsal stripe are specializations cleai'ly in the 

 direction of JiyperytJu us. 



The most emphasized characteristic of lahialis., the contact of the 

 anterior na.sal with the second upi:)er labial, is of lessened importance 

 because of its variability. This feature is often fovnid in other 

 forms of Cnemidophonis, and the contact between these two elements 

 is varied from a mere touching to broad contact in the known speci- 

 mens of lahialis. Moderate contact in a s])eciineii of pcrplexus from 



