DISTRIBUTIONAL PATTERNS OF VERTEBRATES 459 



southwestern refuge, leaving a relict, B. houstonensis , on the eastern 

 Texas coast. 



The Mississippi Embayment also limits the westward distribution 

 of five species of anurans that have no western counterparts. These 

 are the oak toad {Bujo quercicus), bird-voiced treefrog {Hyla phaeo- 

 crypta), barking treefrog {H. gratiosa), little grass frog (//. ocularis), 

 and river frog {Rana heckscheri) . 



The Peromyscus maniculatus group of mice, with one of the most 

 complex distributional patterns of any North American vertebrate 

 (Fig. 11), shows east-west speciation on the coastal plain (Blair, 

 1950). The beach mouse (P. polionotus), which occurs on the coastal 

 plain east of Mobile Bay, on morphological evidence is derived 

 from the grassland-adapted ecotype of the deer-mouse (P. manicula- 

 tus), which today ranges southward into south-central Texas (Fig. 

 11). The beach mouse presumably originated through an eastward 

 dispersal along Gulf Coast beaches and subsequent isolation in 

 Florida. The forest-adapted ecotype of the deer-mouse living today 

 in the southern Appalachians presumably moved south during 

 glacial stages into the area that is today a gap between the range of 

 the beach mouse and that of its Texas progenitor. 



The brown water snake {Matrix taxispilota) , which ranges from 

 Florida into Mexico, has a disjunct population in southern Mexico 

 (Smith and Taylor, 1945). The rat snake (Elaphe obsoleta) shows 

 evidence of secondary interbreeding on the Edwards Plateau in 

 Texas. Turtles of the genus Graptemys are of dubious value here be- 

 cause of lack of agreement among specialists on the group. As 

 mapped by Carr (1952) the range of G. pseudogeographica is mostly 

 west of the Mississippi River, and that of G. geographica mostly east 

 of it. The mud turtles, Ki?tosterno7t, are represented by two species 

 in the eastern forest and three to the west of it (Cagle, 1957). 



The bats have been omitted from the preceding discussion, but 

 they too show east-west disjuncts across the coastal plain. Examples 

 are found in the genera Tadarida, Eumops, Cory?iorhinus, Pipistrel- 

 lus, Dasypterus, and Lasiurus. In Lasiurus, the pattern of distribu- 

 tion is comparable to that of the Peromyscus leucopus group: the 

 western L. borealis overlaps the coastal plain L. seminolus along the 

 forest border in the west and along the Fall Line. 



Some species of vertebrates, showing no evidence of previous dis- 

 junction, range today completely across the Gulf Coast, and conse- 



