608 Original Articles. [Oct., 



Next to these four genera we must arrange the typical form Cebus, 

 in which the tail, though still prehensile and having the terminal 

 vertebrae dilated, is wholly covered with hair, and does not serve the 

 same important office of a fifth hand, as is the case in the Ateline 

 groups. The Cebi have a wide range, from Guatemala on the north, 

 to the banks of the Uruguay in the south. They are very difficult to 

 distinguish specifically, owing to their great variation in colouring. 

 Wagner, in his supplemental volume to Schreber's Sangethiere, 

 reduces the species of this genus to ten, while Reichenbach, in his 

 lately published Natural History of Apes,* recognizes not less than 

 thirty-five ! There can be no doubt that of the two Wagner is 

 much nearest to the mark. 



After Cebus we come to a section in which the tail is lax and 

 villous throughout, and no longer used for prehension. This group 

 embraces the insect-eating genera Nyctipithecus, Callithrix, and Chryso- 

 tlirix. Nyctipithecus contains some three or four species from the 

 great wood region of the interior of South America, remarkable for 

 their owl-like physiognomy and nocturnal habits. Callithrix is a more 

 numerous genus, and rather wider in its distribution, Callithrix 

 personata being said to occur on the banks of the river Parana, north 

 of Corrientes, and two or three other species, besides this, being found 

 in South-eastern Brazil. Chrysothrix embraces three species, two 

 from the Amazon valley, and a third (0. sciurea) from Guiana and 

 Venezuela, but extending up the Panamanic Isthmus as far north 

 as David. f 



All the preceding genera of American Quadrumana have vertical 

 incisors like the Monkeys of the Old World. There remain to be 

 noticed two forms belonging to the Cebidse, peculiar for having their 

 incisors sloping forward like some of the Lemuridaa. These are 

 Pithecia and BracJiyurus. The Sakis (Pithecia) number some seven 

 or eight species, which inhabit various parts of the great Amazonian 

 wood region and Guiana. Brachyurus, distinguished from Pithecia by 

 its abbreviated tail, contains four species, all from the forests of 

 Amazonia. 



The second family of the American Quadrumana, the Hapalidas 

 (Marmosets), comprehends about thirty species, divisible into two 

 genera, Hapale and Midas. They are most numerous in the forests of 

 the interior of South America, ranging as far south as the borders of 

 the Argentine Republic. One species (Hapale wdipus) is common in 

 Chiriqui, Central America, but I am not aware that any member of 

 this family has been known to occur farther north. 



In considering the Neotropical forms of the next great order of 

 Mammals, the Chiroptera, I shall follow strictly the new classification 

 of this group lately proposed by my friend Dr. Peters, of Berlin,^ 

 who has devoted so much time and attention to the study of this diffi- 



* Die Vollst'andigste Natiu'gescliichte der Affen. Dresden. 



t See 'Proc. Zool. Soc./ 1856, p. 139. 



| ' Sitzungsb. Ak. Wiss. Berl.,' 1864, p. 256. 



