monkey and of the allied genera have induced me to think that the 

 American Monkeys with long hairy tails, and with six grinders, may 

 be divided into two very natural subfamilies, characterized by the 

 position and form of the cutting teeth. 



The first of these groups I should propose to call Callitrichina : 

 they have small erect cutting teeth, forming a regular series with the 

 canines. This group contains the genera Callithrix and Chrysothrix, 

 with small diurnal eyes, and Nyctipithecus, vrith large nocturnal eyes. 



The second group, which may be called Pitheciana, have the cutting 

 teeth large, converging together, and separated from the canines by 

 a large space, and their under ones more or less shelving. This group 

 contams three genera, viz. : — 



1 . Pithecia. The fur elongate, dry, harsh ; the tail club-shaped ; 

 the crovra like a vrig, and the chin slightly bearded ; the lower cutting 

 teeth rather shelving. 



This is the genus Pithecia, as restricted by Spix, the Tarkea of 

 Lesson, containing P. monachus, P. leucocephalus, and P. rufiventer 

 of GeoflFroy. 



Spix (tab. 37. f. 4) figured a skull which appears to belong to a 

 species of this genus, but he does not indicate its name. 



2. Brachywus. The fur silky, short ; tail elongate club-shaped ; 

 the crown like a wig, and the chin largely bearded on each side ; the 

 lower cutting teeth are rather shelving ; limb short and straight. Con- 

 taining Cebus satanas of Hoffmanseg, which is the type of Spix's 

 genus. 



Lesson has given the name of Chiropotes to this group, and Cucajao 

 to a second group, established on the Simia melanocephalus of Hum- 

 boldt, which is probably only a badly stuffed specimen of this species. 



Spix, in his work on Brazilian Monkeys, figures a skull which ap- 

 pears to belong to this genus, but it is like several others on the same 

 plate, without any name, t. 37. f. 5. 



3. Ouakaria. The fur short, silky ; tail short, subcylindrical, the 



