AMEEICAK MONKEYS. 395 



not the only, cause of this deficiency. At the same time, it is not 

 quite as easy to account for the present northern limitation. In 

 Mexico, for example, as far as we are able to judge of the general 

 character of the environment, or of the physical conditions govern- 

 ing it, a much more northerly extension might have been assumed 

 than is actually found ; but, possibly, the matter of a particular form 

 of food-supply may have something to do with restriction in this 

 quarter. The semi-continent of Europe, again, whose only simian 

 inhabitant is the Barbary ape already mentioned, in view of the 

 fact that at one time it was the home of various forms of ape, offers 

 another instance of a region apparently suited to the wants of 

 these animals, yet practically entirely deficient in them ; but here, 

 doubtless, the extermination was a part of the general extermina- 

 tion which removed so many of the more distinctive types of Mio- 

 cene and Pliocene mammals into other regions, whatever the exact 

 cause may have been. 



The New World monkeys are generally all included in two fam- 

 ilies : the Cebida?, with several sub-families, monkeys with thirty- 

 six teeth, and the Hapalidse, or marmosets, monkeys with thirty- 

 two teeth. The former comprise the sapajous (Cebus), which may 

 be taken as the representative genus of American monkeys, the 

 woolly monkeys (Lagothrix), spider-monkeys (Ateles, and the re- 

 lated Eriodes), howlers (Mycetes), sakis (Pithecia and Brachyurus), 

 night-monkeys or douroucoulis (Nyctipithecus), squirrel-monkeys 

 or saimiris (Chrysothrix), and the related Callithrix. The total 

 number of species known is between seventy and eighty, of which 

 about twenty are sapajous, fifteen spider-monkeys, ten howlers, and 

 about an equal number members of the genus 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 ex- 

 tended 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, spider-monkeys, 

 howlers, and callithrixes. The range of the species, on the other 

 hand, is not infrequently very sharply defined, as, for example, 

 when a natural barrier, offering insurmountable obstacles to fur- 

 ther migration, suddenly interposes itself. Examples of such 

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



