144. Ona new Marmoset from the Peruvian Amazons. 
more slender skull, and no naked gular patch in the female. 
It is to be hoped that male specimens will shortly be obtained, 
so that the pouch-structure in that sex can be observed. 
Major Stevenson Hamilton states that the specimen was 
captured in the verandah of his house. 
XVII.—A new Marmoset from the Peruvian Amazons. 
By OLDFIELD ‘THOMAS. 
(Published by permission of the Trustees of the British Museum.) 
Leontocebus mounseyt, sp. n. 
Closely allied to LZ. apiculatus, Thos.*, with which it agrees 
in all essential characters, but distinguished by the following 
points :—Terminal ticking of nape-hairs commencing rather 
further forward, en the hairs between the ears instead of 
further down the neck. Dorsal marbling rather more coarsely 
conspicuous. Fur of under surface, including groins and 
inner sides of thighs, longer and denser, and the hairs all 
with distinct blackish bases instead of being wholly reddish. 
Upper side of hands and feet rather more prominently grizzled 
with fulvous. ‘Tail, beyond its basal reddish-mixed inch, 
abruptly deep black, without any trace of the more extensive 
fulvous grizzling for three or four inches which forms so 
marked a characteristic of L. apiculatus. 
Dimensions of the type (measured in flesh) :— 
Head and body 175 mm.; tail 800; hind foot 58; 
ear 24. 
Skull: gnathion to occiput 46. 
Hab. Rio Pacaya, opposite Sapote, Lower Ucayali. Alt. 
250 feet. 
Type. Adult male. B.M. no. 20.1. 9.1. Original num- 
ber 2. Collected 25th July, 1912, by Mr. J. J. Mounsey. 
One specimen. 
Of the various characters above noted, the most marked is 
the difference in the extension of the grizzling of the base 
of the tail—a character quite constant in other species and 
one that seems certainly to justify the distinction of the 
Pacaya marmoset. 
* Ann. & Mag. Nat. Hist. (7) xiv. p. 190 (1904) ; Elliot, Primates, i. 
p. 204 (1918). 
