128 ALLEN'S NATURALIST'S LIBRARY. 



families, have thirty-six teeth. The former include the Mar- 

 mosets (Hapale) and the Tamarins (Midas). The latter 

 comprise the Capuchins (Cebus), which may be taken as 

 the representative genus of American Monkeys, the Woolly 

 Monkeys (Lagothrix), the Spider-Monkeys (Ateles and the 

 allied Eriodes), the Howlers (Mycetes), the Sakis (I'ithecia and 

 Brachyurus), the Night-Monkeys or Douroucolis (Nyctipithecus), 

 and the Squirrel Monkeys or Saimiris (Chrysothrix), with the 

 allied Callithrix. 



"The extensive equatorial forests of the Amazon and 

 Orinoco, and their tributaries, constitute par excellence the 

 home of the American Monkeys, but the majority of the 

 genera have a very extended range, appearing in one or more 

 species throughout the greater portion of the tract covered by 

 the entire family. This is more particularly the case with the 

 Sapajous (Cebus), Spider-Monkeys, Howlers, and the species of 

 Callithrix. The range of the species, on the other hand, is 

 not unfrequently very sharply defined, as, for example, when 

 a natural barrier, offering insurmountable obstacles to further 

 migration, suddenly interposes itself. Examples of such limita- 

 tion, as brought about by the dominant water-courses of the 

 equatorial forests," are numerous. Mr. Wallace cites the case 

 of certain species of Saki Monkey (Pithecia\ found on either 

 side of the Amazon river, whose range, either southward or 

 northward, appears to be limited by that river. "The number 

 of species of these American Apes found in, and north of, the 

 Isthmus of Panama is ten, of which only one (Ateles vellerosus) 

 extends into Mexico ; Mycetes vH/osus, the Guatemalan Howler, 

 or ' Mono,' has thus far been found only in Guatemala and 

 Honduras. It is a little surprising that the range of only two 

 of the species the Black-faced Spider-Monkey (Ateles ater) 



