Zoological Society. 55 



eminent zoologists as a species of Cehus which had lost part of its tail ; 

 but there was a peculiarity in the position of the thumb as regarded 

 the fingers, which at once showed that whatever might be the natural 

 length of its tail, it evidently did not belong to the genus Cehus as at 

 present restricted. The examination of the animal after death showed 

 that it was a most distinct genus, and nearly related to, if not a variety 

 of, Brachyurus Ouakari of Spix. 



I may observe that the genus Brachyurns was established by Spix 

 in his work on American Monkeys for two species, viz. 1 . the Simla 

 Chiropotes of Humboldt (the S. Sagulata of Trail), which has been 

 generally referred to the genus Pithecia ; and 2. Brachyurus Ouakari. 

 Spix in the same work restricted the genus Pithecia to the Saki or 

 Long-haired American Monkeys. 



The examination and comparison of the skull of the short-tailed 

 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 Chrysothrisc, 

 with small diurnal eyes, and Nyctipithecus, with 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 

 contains three genera, viz. -. — 



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

 the crown like a wig, and the chin slightly bearded ; the lower cutting 

 teeth rather shelving. 



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

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

 of Geoffroy. 



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. Brachyurus. 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 Cehus 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 

 crown with short hair ; the chin scarcely bearded ; the lower cutting 

 teeth very much shelving ; legs elongate. 



This genus forms part of the genus Brachyurus of Spix ; and if 

 Spix had not evidently described the teeth, &c. of his first species in 



