FIG. 3. Distribution of the karyotypic forms of Sceloporus grammicus in the Valley of Mexico region. A. The Valley of Mexico. B. The Rio Frio study area. Locality symbols are the same as in Fig. 2. Areas where individuals with hybrid karyotypes have been found are indicated with H's in A and with cross-hatching in B. In B the inferred position of the zone of hybridization is indicated by heavy shading. Numbers by locality symbols indicate number of specimens karyotyped.