452 W. F. BLAIR 



and animals that are disjunct from their main populations. The 

 palmetto {Sabal minor), burr oak {Quercus macrocarpa) , wax myrtle 

 (Myrica cerifera) and ash {Fraxinus) are representative of a rather 

 large number of plants in this category. The vertebrates include 

 the canebrake rattlesnake {Crotaliis horridus), banded watersnake 

 (Natrix sipedon), and narrow-mouth frog (Microhyla carolmensis) . 



PRESENT PATTERNS OF DISTRIBUTION 



The vertebrate groups of the coastal plain under consideration are 

 characterized with few exceptions by a relative scarcity of closely 

 related sympatric species and by a rather large number of allopatric 

 species or populations that show evidence of relatively recent dis- 

 junction. Among the 40 genera of mammals, only seven include 

 species that are sympatric on the coastal plain. The best represented 

 genus is Peromyscus, with five species that represent three subgenera. 

 The lizard fauna is sparse, with only eight genera, of which three, 

 Sceloperus, Eumeces, and Ophisaiirus, include species that are 

 sympatric there. On the coastal plain, there are 25 genera of snakes 

 of which nine there include sympatric species, with the largest 

 representation in the genus Natrix. Four of the 13 genera of turtles 

 include species that are sympatric on the coastal plain. Five of the 

 seven genera of anurans include species that are sympatric on the 

 coastal plain, but only Ra?ia and Ilyla, which have their United 

 States center of distribution on the plain, include several species 

 that are broadly sympatric there. Six of the 12 genera of urodeles 

 include species that are sympatric on the coastal plain. 



If the urodeles are excluded from the tabulation the some 40 

 cases of allopatry, secondary interbreeding, or narrow sympatry 

 indicative of past separation into east and west populations out- 

 number the cases indicative of north-south disjunction in a ratio of 

 more than seven to one. These east-west disjunctions follow a few 

 general patterns. One pattern involves present limitation of the 

 disjunct populations to forests. One example is that of Pitymys 

 (Fig. 6), which was mentioned earlier. Another example is furnished 

 by the flying squirrel (Glaucomys volans), which ranges west to the 

 border of the eastern deciduous forest and has a disjunct subspecies 

 in the mountains from Chihuahua to Honduras (Martin and Harrell, 

 1957). The opossum {Didelphis marsupialis) shows evidence of 

 secondary interbreeding of previously disjunct populations in 



