CROCODILIANS, LIZARDS. AND SNAKES. 1209 



tiiiled forms. The majority of species of the tailless genera me found 

 here, esi)eci}il]y of Ilyla (tree toads). Nana, and Ghorophilus. 



There are no less than nine genera of birds which do not, oi- only 

 accidentally, range northward of this district. They are, according to 

 Allen: 



Plains. Gonurns. 



Tantahia. Cli ama'peUa. 



Plotalea. Campephiluti. 



Elanns. Helhuca. 

 Jctinia. 



All these genera, excepting the last, rang»^ into South America or 

 further. 



Among mammals, but few species and one genus [Sifimodon) are con- 

 fined to it. Lepvs (ujnaficns and L. jfolusfris, the cotton rat, etc., and a 

 few others, are restricted by it. The tish fauna Is very similar to that 

 of the Eastern region. 



The Eastern si(hre(/ion ditt'en^ from the Austrori])arian almost entirely 

 in what it lacks, and agrees with it in all those peculiarities })y which it 

 is so widely separated from the Sonoran subregion. No genus of mam- 

 mals is found in it which does not range into other regions, excepting 

 the Insectivorous genera Parascalops and Gondylnra (star-nosed mole); 

 but numerous species are confined to it, not extending into the Austro- 

 rii)arian. These number from twenty to twenty-five. Among birds, 

 the following genera are, according to J. A. Allen, share<l with the more 

 southern region only: Quiscalus, ^ixrus, Relmitherns, Protonotarm, 

 Parula, Mniotilta. ^o genus of Kej)tiles, and but one of Batrachians 

 (Gyrinophilus), is confined to this region; but it shares all it possesses 

 with the Austrorii)arian. It has but four genera of lizards, namely, 

 Sceloporus, Gnemidopltorus, Liolepisma, and Eumeces. 



The Sonoran subregion is cliaracterized in the lower vertebrate fauna 

 by great poverty in fishes, batrachians, and tortoises, and abundance 

 of lizards and snakes. Among fishes it lacks the orders (iinglymodi, 

 Halecomorphi, and Choudrostei, and possesses only one peculiar group, 

 the PlagO|)terina% a division of the Cyprinida'. Of usual llolarctic 

 types it possesses only rsos[)ondyli (Salmonida') and Plectosi)ondyli ; 

 Percomorphi and Nematognathi being absent. The rivers that inter- 

 sect its central district contain these types, but they must be reckoned 

 as belonging with their bottom lands to the Eastern subregion; the 

 high i)lains only belonging to the Sonoran. The true drainage area of 

 the Sonoran subregion is that of the Colorado. 



No genus of Batrachia is peculiar to it, and the following divisions 

 are wanting: Proteida, Trachystomata, Amphiumoidea, an<l all (Tro- 

 dela, except Amblystomida' (one species). The genus Bu/o is the 

 only one that is well represented. 



