158 ALLEN’S NATURALIST’S LIBRARY. 
IV. THE RED-BACKED TITI. CHRYSOTHRIX CERSTFDI. 
Satmaris scturea ? (nec Linn.), Sclater, P. Z. S., 1856, p. 139. 
Chrysothrix scturea (nec Linn.),Scl., N. H. Rev., 1861, p. 510; 
Frantz. Arch. f. Naturg., xxxv. (1), p. 260. 
Chrysothrix erstedi, Reinh. Vidensk. Medd. Nat. For. 
Kjobenh., p. 157, pl. ili. (1872); Alston, in Godm. et 
Salv., Biol. Centr. Am. Mamm., p. 16, pl. ii. (1879). 
Saimiris entomophaga, Sclater, P. Z. S., 1872, p. 3 (nec 
d’Orb.). 
Saimiri orstedit, Schi., Mus. Pays Bas, vii., p. 245 (1876). 
Characters.—Differs from C. sczuvea in having the top of the 
head black, the back and sides shining red, and the limbs 
olive, 
Distribution Panama, Guatemala, Costa Rica, especially their 
hotter districts,;—being particularly abundant in the Valley 
of Terraba and on the plain of Piris. 
THE TITI MONKEYS. GENUS CALLITHRIX. 
Callithrix, Geoffr., Ann. Mus., xix., p. 112 (1812). 
This genus is intermediate between the Squirrel-Monkeys 
and the typical Night-Monkeys. In the Titis, sometimes 
known by the name also of Whaiapu-Sai Monkeys, the fur is 
sott, the head small, depressed, and not produced backward 
as in Chrysothrix ; the tail is long and bushy; the eyes are 
small, and the orbits intermediate in size between those of the 
last and the next genus; the nasal partition is broad, and the 
ears large. The canine teeth are small, and the angle of the 
lower jaw expanded, somewhat as in the Howlers (JZyce/es), 
though to a less extent. 
