198 



BULLETIN" 15 4, UISriTED STATES NATIONAL MUSEUM 



Affinities. — Because of its characters, geographical position and 

 plasticit^y, tesscUatus is obviously the stem-form of its group. For 

 reasons to be presented in the general summary at the end of this 

 Avork (pp. 251-260), it is thought to have been descended (either 

 directly or through maxiinus) from gularis of the sexUneatus group 

 from which its color pattern may V.>e logically and simply derived, 

 and with which it agrees in all fundamentals of scutellation, except- 

 ing for a notable decrease in the average size of the post-antebra- 

 chials. 



In scutellation it is " almost identical with serdineatus,''^ as stated 

 by Brown (1903, p. 547), but its coloration suggests only certain 

 phrases of gularis. In this respect, just why Ellis and Henderson 



rubidus 



airt\[r\i 



c-gm-us 



• t^&sellail-us 



mB^xiTrwAS 



Ancestral Stock of tV»e TesseUalxis Groxip 



FlGUUE L'S. 



-ItlAGUAH OF THE SUW'OSED UlCLATIONSIIirS OF C. TESSET-LATUS 

 TESSELLATUS 



(1913. ]>. 77) sliould have written that " The young tessellated lizard 

 is marked much like the adult sexUneatus " is not apparent. Strecker 

 (1908, p. 169) has correctly reported that the sides of an adult male 

 of gularis may present a barred and mottled appearance as seen in 

 some examples of tessellatus. This is at once evident to those work- 

 ing with series from various localities, particularly from western 

 Texas and Chihuahua. 



The large maximus is apparently not closely related to the modern 

 tessellatus. It is probable that both forms represent a common stock 

 and that they were differentiated before the birth of any of the other 

 known forms of the group. At the southern part of its range in 

 Lower California, tessellatus seems to have ver}^ recently given rise 

 to ruhidus with which it now intergrades. In the Gulf of California, 

 tlie insular subspecies, martyris and canus, have become distinguish- 

 able on very slight, although apparently constant, characters, and 

 their evolution from the parent stock seems to have been compara- 

 tively recent. Their relationship with tessellatus has been discussed 



