462 W. F. BLAIR 



However, evidence inconsistent with such an explanation is pro- 

 \'ideci by the numerous hiatuses between eastern and western 

 populations that involve segments of one or the other environments 

 or segments of both. 



Sympatric distributions of coastal plain groups may trace back to 

 the same kind of east- west disjunction exhibited by the allopatric 

 populations, but such history is difficult to demonstrate. McConkey 

 (1954) has theorized that the three species of legless lizards (Ophi- 

 saurus) of the coastal plain originated through east-west splitting 

 in the Third Glacial (Illinoian) and through subsequent isolation of 

 the third population on Florida islands in the Third Interglacial 

 (Sangamon). 



DISTRIBUTIONAL PATTERNS OF ANURANS AND URODELES 



A comparison of the distributional patterns of anuran and urodele 

 amphibians in the eastern United States illustrates as clearly as any 

 possible documentation the postulated Pleistocene history of the 

 coastal plain biota. The anurans are mostly a warmth-adapted 

 group, with more species on the coastal plain than anywhere else in 

 the United States. Ten of the 24 coastal plain species or species 

 groups show evidence of past or present disjunction into eastern and 

 western populations, as discussed in the preceding section. Seven of 

 the 10 have their eastern population limited to the coastal plain. 

 The other three, Biifo woodhousei, Pseudacris nigrita, and Hyla 

 versicolor, range widely in the eastern United States. Six of the 

 remaining 14 species are limited to the coastal plain east of the 

 Mississippi Embayment and are presumed to have spread to their 

 present limits from a Pleistocene refuge in Florida. Of the eight 

 remaining species, only three are limited to the coastal plain. Two 

 of these, Hyla cinerea and H. squirella, range across the coastal plain 

 from the Atlantic to Texas, and the range of the third, Rana grylio, 

 stops short of the forest border in eastern Texas. The five remaining 

 species, Hyla crucifer, Rana pipiens, R. palustris, R. clamitans, and 

 R. catesbeiana, all range northward into Canada, and on the basis 

 of their present distribution it seems likely that they could have 

 existed continuously across the coastal plain under Pleistocene 

 Glacial-stage conditions. North-south speciation in the anurans is 

 limited to the splitting off of Hyla andersoni and the speciation in 

 the Pseudacris nigrita complex discussed earlier. 



