396 GEOGRAPHICAL AKD GEOLOGICAL DISTKIBUTIOK. 



equatorial forests, have already been noticed in treating of specific 

 distribution in general (pp. 23, 24). The number of species found 

 in, and north of, the Isthmus of Panama is ten, of which only one, 

 the spider-monkey already referred to, extends into Mexico ; My- 

 cetes villosus, 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) and one of the night-apes (Nyctipithecus vo- 

 ciferans) extends beyond Colombia in South America. 



None of the South American monkeys appear to pass west of 

 the Andean chain of mountains south of Ecuador, and even north 

 of the Peruvian boundary the number of such transgressional forms 

 is very limited. Indeed, even among the wooded slopes, a habita- 

 tion along the basal line of the mountain axis seems to be much 

 preferred. The greatest altitude at which monkeys were observed 

 by Tschudi in Peru was 3,000 feet (Lagothrix Humboldtii) ; Ateles 

 ater and Cebus robustus were found at 2,500 feet. On the other 

 hand, Godman and Salvin state that in the district of Vera Paz, in 

 Guatemala, the mono or howler is most abundant at an elevation of 

 6, 000 feet ; and on the volcano of Atitlan, in the same country, Mr, 

 Salvin found troops of the Mexican spider-monkey (Ateles vellero- 

 sus) in the forest region of 7, 000 feet elevation. 



The range of the marmosets and oustitis (Hapalidae) is nearly 

 coextensive with that of the monkeys proper, but no form is thus 

 far known to pass beyond the Isthmus of Panama ; * Midas Geof- 

 froyi alone inhabits the Isthmus. The species, of which there are 

 some thirty or more referable to two genera (or sub-genera), Midas 

 and Hapale, are most numerous in the equatorial forests. 



Of the Old World Quadrumana, the anthropoid apes (Simiinae), 

 which include the gorilla, chimpanzee, gibbon, and orang, acquire 

 special importance by reason of their high structural organisation. 

 In the sum of all their characters, the gorilla probably stands the 

 highest, although by many naturalists this place is conceded to the 

 chimpanzee. Only one species of gorilla (Troglodytes gorilla) has 

 thus far been positively determined, but not impossibly other 

 forms may inhabit the interior ,of the African continent. The rec- 

 ognised habitat of the species is the west coast of Africa a few de- 



* Midas rufiventer, erroneously described as coming from Mexico, is a Bra- 

 zilian species (M. labiatus). 



