1204 



REPORT OF NATIONAL MUSEUM, 1898. 



with tlie Neotropical, which do not occur iu the Ethiopian. These 

 are the Arciferous Batrachia, the Crotalid snakes, and the deer 

 (Gervidte), The Medicolumbian division of the Holarctic shares other 

 forms with the Neotropical. These are Didelphyidjie and Procyonida' 

 among Mammalia; Tyraunid, Icterid, and Tanagrid birds; Cinosternid 

 tortoises, and the Arciferous Batrachian family Hylidas. 



Some of the forms of the Holarctic region are not uniformly dis 

 tributed over it. Thus the Gingiymodous and Polyodontid lishes only 

 occur in the eastern parts of the eastern and western continents. The 

 same is true of the Siluroid genus Amelurns and the Loricate genus 

 Alligator. The Crotalid snakes are not found in the western part of 

 Eurasia. The Batrachian Cryptobranchidaj have the same distribu- 

 tion. 



The Medicolumbian Region. 



This region was formerly included in the Nearctic of Sclater, and the 

 area thus constituted has the following geographic boundaries: To the 

 south it includes the plateau of Mexico, including the central valley. 

 The Neotroi)ical area bounds it to the east and west, occupying the 

 lowlands, or Tierra Caliente, to a point 150 miles south of the Eio 

 Grande on the east,' and to Mazatlan, or some point not far from it, on 

 the west. The high laud of Oaxaca is its extreme southern outpost. 

 Its northern boundary is thus described by Merriam: ^ 



Tlio Boreal (Holarctic realm) Province extends oblu^uely across the entire con- 

 tinent from New England and Newfoundland to Alaska, conforming in direction to 

 the trend of the northern whores of the continent. It gives otf three long arms or 

 chains of islands which reach far south along the three great mountain systems of 

 the United States, a western arm in the Cascades and Sierra Nevada, a central arm 

 in the Rocky Mountains, and an eastern arm hi the Alleghanies, and these interdig- 

 itate with northward prolongations of the Sonoran (Medicolumbian) province, which 

 latter completely surrounds the southern islands of the Boreal (Holarctic) system. 



The faunal relations of the Medicolumbian realm may be tabulated 

 as follows : 



Agrees with Holarctic in — 



Differs from Palearctic in- 



Peculiar forma. 



Neotropical forms. 



Maimiialia in general . 



Excei)t 



Birds, except . 



(i Antiloca 

 V Mephitis 

 t Talpidii! 



MeleagridsB. 



Kmyd t ortoises Chelydra . 



Lache.sinse Crotalin». 



BassarididfB. 



Procyonida;. 



Megadermatid;c. 



Dicotyles. 



Didelphys. 



CathartidsB. 



TanagridaB. 



Icterida>. 



Claniatores in general. 



Trochilidae. 



Odont(ii)horina^. 



Alliigators. 



Teiid and Gerrhonotid lizards. 



Igiianid lizards. 



Cinosternidai. 



Elapid venomous snakes. 



' Townsend, Texas Academy of Science, 1895, p. 87. 



2 Biological Survey of the San Francisco Mountain; North American Eauna, No. 

 3, 1890, p. 24. 



