THE TAXONOMY AND BIOGEOGRAPHY OF THAMNOPHIS-HAMMONDII AND T-DIGUETI (REPTILIA, SQUAMATA, COLUBRIDAE) IN BAJA-CALIFORNIA, MEXICO

The taxonomic status of Thamnophis hammondii and T. digueti was reeval uated using characters of squamation and color pattern. A comparison o f scale counts using discriminant function analysis and a Student-Newm an-Keuls multiple range test and the presence or absence of certain co lor pattern characters demonstrate that T. digueti is an invalid taxon . Therefore, it is placed in the synonymy of T. hammondii. It appears that T. hammondii was once broadly distributed in Baja California and has since become isolated in mesic refugia due to xerification of cent ral peninsular regions. Similar patterns of distribution are also obse rved in other transpeninsular mesophilic taxa.