90 BIIJ.LETIX 15 4, UNITED STATES NATIONAL MUSEUM 



sexlineatiis is one of the more specialized forms, and that it has 

 descended from (jularis-fevplexii^ stock. Either theory might be 

 correct, but for reasons to be given in the general discussion at the 

 end of this work, it is apparently best to accept the latter one. It 

 seems ver}^ probable that Barbour and Noble (1915, p. 420) are cor- 

 rect in saying that change of climate " forced the ancestral Teiids 

 soutliAvard and they liourished and are now wholly confined to the 

 tropics, except sexlineatus, wliich has secondarily invaded the Aus- 

 troriparian zone of North America, and a few species which have 

 pushed into temperate South America." Thus, even though the 

 Teiidae originated in the north as suggested by Matthew, sexlineatus 

 may have become modified from a southern ancestral stock before 

 its secondary invasion of the eastern part of the United States. 



This species retains the juvenile type of coloration everywhere, 

 as shown by Cope (1900). It seems that Brown (1903, p. 547) was 

 correct in maintaining that the scutellation of tesseUatus is " almost 

 identical " with that of the present form. Because of a fundamental 

 ditference in color pattern, the two are placed in different groups 

 here, but are listed as coming from the same ancestral stock. In 

 spite of the resemblances, it is surprising that Ellis and Henderson 

 (1913, p. 76) should have written that the young of tesseUatus are 

 marked much like the adult of seoeUneatus. 



The intergradation between fevflexus and sexlineatus is confined 

 to a small area in western Texas and Oklahoma and possibly in 

 eastern New Mexico, and in some cases gularis-perplexus intergrades 

 are almost identical with sexlineatus- per plexiis intergrades, as at 

 Pecos in western Texas, so the problem arising in this region is very 

 complex. The intergradation between sexlineatus and gulwris oc- 

 curs over an elongated line of contact and is much more extensive, 

 apparently, than that of perplexus with gularis. This is due, per- 

 haps, to a sharper delineation of habitat differences in the latter 

 case, as well as to other factors. From the geographical position and 

 proportional extent of intergradation, it seems that both sexlineatus 

 and perplexus have risen from the central givlaris. The intergrada- 

 tion between sexlineatus and perplexus is apparently only secondary, 

 rather than primary like the intergradation of each of these forms 

 and gularis. This is supported by the fact that the yellowish mid- 

 dorsal streak of sexlineatus occurs just as frequently in gularis, but 

 disappears in perplexus, and that spots are often found on the sides 

 of perjdexus and givlaris, but disappear in sexlineatus. 



Although Ellis and Henderson (1913, p. 76) claimed that " The 

 young of gularis are marked much like the adult of sexlineatus,^'' it 

 is found that spots are present in the lateral fields of some of the 

 youngest specimens of gularis from certain areas and that they are 



