74 BULLETIN 15 4, UNITED STATES NATIONAL MUSEUM 



Although guttatus is not found south of Mexico, deppii ranges 

 south to Costa Rica, so during the submergence of the Tehuantepec 

 region deppii is presumed to have remained unchanged or to have 

 developed in Central America, whereas gwttatits changed and evolved 

 in southern Mexico. A secondary union of the land masses involved 

 would have made it possible for the more plastic dej>pii to migrate 

 northward into Mexico and not only to extend its range throughout 

 the favorable area there occupied by guttatus but also to extend it 

 northward along the Pacific slope, past the range of that form, into 

 Colima and Nayarit as well. Such an explanation may also account 

 for the great overlapping in the ranges of the closely related Ameiva 

 undulata and Ameiva f estiva which are also found in Central Amer- 

 ica and Mexico. The foregoing diagram (fig. 17) is intended to 

 illustrate the manner in which guttatus and deppii as closely related 

 forms have assumed their present coextensive distribution. 



SUMMARY OF THE DEPPII GROUP 



The deppii group is confined to Mexico and Central America. Its 

 representatives are alike in scutellation and resemble each other in 

 color pattern, but the adult size is variable. There are three forms, 

 deppii^ cozmnelus^ and guttatus. In searching for the prototype 

 among these one has to consider only deppii and guttatus since 

 cozumelus is an insular form which has obviously been recently iso- 

 lated and derived from deppii. The remaining two forms are like- 

 wise closely related, but deppii is thought to be the older unit because 

 of its much closer geographical and colorational approach to lemni- 

 scatus with A^'llich it agrees in size and from the stock of which the 

 deppii group is obviously derived. 



Since a consideration of the genetic origin of the group as a whole, 

 and hence of the prototypic deppii., is given in the general discussion 

 at the end of this work (pp. 251-260), the present consideration will 

 be limited to the origin and relationshij^s of the two derivatives, 

 cozwnelus and guttatus. 



Gozumelus is known only from the islands of Cozumel and Mujures 

 off the coast of Quintana Roo in southern Mexico. These islands 

 are very near to the mainland and the lizards are small like deppii., 

 differing from it only in a slight but apparently coustant modifica- 

 tion of the color pattern. Because of this, and since guttatus and 

 gulai'ix, the other possible ancestors, differ greatly in size and scutel- 

 lation, respectively, cozumelus is thought to be a direct descendant 

 from a common stock with deppii. 



The remaining form, guttatus, occurs only on the Mexican main- 

 land. Because of its striking similarity to deppii and its obvious 



