1894. NEARCTIC OR SONORAN ? 55 



Nyctinojuus, and Felis occur also in the Palaearctic Region. The 

 remaining twenty-seven are peculiarly American, and it will be seen that 

 this number is just over two-thirds of the thirty-nine given in the third 

 column of Dr. Wallace's table as the number of Nearctic genera not 

 to be found in the Old World, The peculiar family of the Pouched 

 Rats (Geomyidae) is specially noteworthy as coming distinctly into the 

 Sonoran fauna, only one of its genera {Tlwinomys) just entering the 

 Boreal Region. The other peculiar mammalian family, Antilocapridae 

 (Prong-horn), is also seen to be typically Sonoran. The differences 

 between the two mammalian faunas in North America may now be 

 shown in tabular form : — 



Distinctively ^°^^'^°^ I^^^^'^^'"'^ 

 American. Pal^arctic Region. 



Genera common to Boreal and 



Sonoran Regions . . 2 " 6 



,, typically Boreal . . 10 20 



,, ,, Sonoran . . 27 5 



And it becomes clear that the affinities of the northern fauna of 

 America are with the fauna of Europe and temperate Asia, while the 

 Sonoran fauna is exceedingly distinct. 



When we turn to the birds we find, as might be expected, that 

 the regional divisions are not so closely kept as by the mammals. 

 Nevertheless it is possible, by a survey of the distribution of each 

 genus, to determine to which fauna it belongs. A genus with 

 several Sonoran species and but one Boreal may fairly be reckoned 

 as Sonoran. In compiling the following summary I have taken the 

 distribution as given in the A.O.U. Check List, whence Dr. Wallace 



compiled his genera : — 



-r. Common to America 



Distinctively 



American. Pal^arctic Region. 



Genera common to Boreal and 



Sonoran ...... 30 32 



Typical Boreal genera . . 2 '^ 14 ^ 



Sonoran ,. .. 81 » 8" 



It is not necessary to give lists of all these genera. I give in the 

 footnote their reference numbers in Dr. Wallace's lists, which will 

 enable anyone interested in the subject to check my results. 



It will be seen that of the hundred and thirteen genera of birds 

 which, according to Dr. Wallace, diflferentiate the Nearctic from the 



'' One of these [Otaria) is not. peculiarly American. 



■^ Genera nos. 34, 35 (3rd col). 



** ,, ,, 18, 20, 21, 22, 23, 25, 26, 27, 31, 36, 37, 47, 53, 54 (2nd col.). 



^ .. >. 3. 4f 5, 6, 7, 8, 9, 10, II, 12, 13, 15, 16, 17, 18, 19, 23, 26, 28, 32, 



33. 37. 41. 42. 46. 47. 48, 49. 50. 51. 52, 53. 54. 55. 56. 57. 59. 

 61, 62, 63, 64, 65, 66, 67, 68, 70, 71, 72, 74, 75, 77, 78, 79, 80, 

 81, 82, 83, 85, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 

 102, 103, 104, 105, 106, 107, 108, 109, III, 113 (3rd col). 



1° ,, ,, 6, 7, 8, 29, 33, 41, 49, 52 (2nd col.). 



The sixty-two genera not enumerated here are common to the Boreal and 

 Sonoran tracts. 



