144 BULLETIN 15 4, UNITED STATES NATIONAL MUSEUM 



southern Arizona lead Van Denburgh {ISdGh, p. 344) to describe it 

 as a new species, C arisonae. This specimen of 'perplexus^ hke many 

 others, has a strong resemblance to labmUs, and differs merely in the 

 increased number of femoral pores, in the color of the sides, and in a 

 more stable character of the dorsal striping. 



Thus, lahialis may be considered as a derivative of ferplexus stock, 

 specialized somewhat in the direction of hyperythrus. 



SUMMARY OF THE SEXLINEATUS GROUP 



The sexUneatus group is largely confined to the mainland of the 

 United States, Mexico, and Guatemala. Representatives occur on 

 some of the bordering islands off the coast of southern Mexico, west- 

 ern Lower California, Texas, and the eastern United States, but they 

 are absent from most of the islands in the Gulf of California. All 

 of the forms agree in having the sides of the young striped, and in 

 the normal possession of two frontoparietal plates and four 

 supraoculars. 



The group is composed of four forms, gularis^ the only one from 

 which the remaining members can be easily and simply derived, and 

 its three mainland derivatives, sexUneatus^ perplexus, and lahialis. 

 A consideration of the genetic origin of the group as a whole, and 

 hence of the prototypic gularis, is given in the general summary at 

 the end of this work (pp. 251-260), so the present discussion will l)e 

 limited to the origin and relationships of the three derivatives. 



The range of gularis is clearly intermediate between that of the 

 remainder of the sexUneatus group and that of the modern repre- 

 sentatives of the presumably more primitive depp'd and lemniscatus 

 stocks, Gularis in its present area is geographically intermediate 

 between the eastern off-shoot, sexUneatus, and the western derivatives, 

 perplexus and lahialis, and many intergrading individuals between 

 sexUneatus and gularis, and between gularis and perplexus, have been 

 examined. SexUneatus was apparently independently derived from 

 gularis stock in eastern Texas and, although it has differentiated and 

 spread as a distinct form throughout the lower levels of the eastern 

 United States, including the southeastern coastal plain, it still inter- 

 grades with gularis in southern Oklahoma and in eastern Texas. 

 Since there is little contrast in the types of habitat found in this 

 region, there is no sharp delineation of tliese subspecies here and the 

 resulting belt of intergradation is therefore unusually wide. In the 

 Panhandle region of Texas and Oklahoma gularis and sexUneatus 

 approach perplexus, both geographically and in their characteristics, 

 and probably all three subspecies intergrade here. Lack of specimens 

 prevents further elaboration or proof of this theory. Since perplexus 

 occupies the arid Sonoran region and since intergrades appear in a 



