156 ALLEN'S NATURALIST'S LIBRARY. 



In some species the upper part of the head has a shade of 

 yellow, caused by the colour of the lower half of the hairs 

 showing through the black tips. 



Distribution. Bolivia; Veragua, Central America; and the 

 warmer regions of Costa Rica, where it inhabits the humid 

 forests. 



III. THE COMMON SQUIRREL-MONKEY. CHRYSOTHRIX 

 SCIUREA. 



Simia sa'urea, Linn., Syst. Nat., i., p. 43 (1766); Humb., 



Obs. Zool., p. 334 (var. cassiquiarensis). 

 Callithrix sa'ureus, Geoffr., Ann. Mus., xix., p. 113 (1812). 

 Saimiri sa'ureus, Cuv., Reg. An., p. 103, pi. i (1829); Schl., 



Mus. Pays Bas, vii., p. 242 (1876). 



Chrysothrix lunulata, Geoffr., Arch. Mus., iv., p.\i8 (1844). 

 Chrysothrix sa'urea, Wagner in Schreb., Saugth. Suppl., v., 



p. 120, pi. 9, (1855); Gray, Cat. Monkeys Brit. Mus., p. 



53 (1870); Sclater, P. Z. S., 1880, p. 395. 

 Chrysothrix nigrivittata, Wagn., Abh. bay. Ak. Miinchen, 



v., p. 461. 



Characters. Smaller than the two preceding species ; face 

 greyish-white ; chin round and prominent ; head blackish- 

 grey ; back grey, or grey washed with gold, the basal part of 

 the hairs golden and the tips black ; outer side of the fore-arm 

 yellow; tail long, slender, grizzled grey, with the tip black. 

 Length of the body, 10 inches; of the tail, 14 inches. 



Certain females, examined by Dr. Sclater, had a distinct 

 black line along the side of the crown above each ear and ex- 

 tending in front, down the side of the face, nearly to a level 



