Forms of Saimiri, Saccopteryx, &c. 251 



elbow. Feet edged on eacli side witli orange, and the toes 

 are also the same colour, but the middle line of the meta- 

 tarsus is grizzled greyish, continuous with the greyish of 

 the legs. Proximal part of tail grizzled grey like the limbs, 

 less yellowish than in Oerstedi; end of tail black as usual. 



Dimensions of the type (measured in skin) : — 



Head and body 350 mm. ; tail 415 ; hind foot 90. 



Skull : greatest length 65 ; breadth of brain-case 36. 



Hab. Costa Rica. Type from Pozo Azul, Pirris. 



Type. Adult male. B.M. no. 4. 2. 7. 2. Collected 31 May, 

 1902, by Mr. C. F. Underwood. Six specimens. 



The Squirrel-Monkey of Costa Rica has long been known, 

 and this very locality, Pirris, is mentioned in Dr. von 

 Frantzius's account * of the distribution of what he called 

 " Chrysothrix sciurea" identified by Alston with 8. Oerstedi. 

 But a comparison of the series sent by Mr. Underwood with 

 those representing the true Oerstedi^, collected in Panama 

 and Veragua by Messrs. Watson, Batty, and Arce, shows 

 that the northern form differs constantly from the southern 

 in certain characters. Of these the most tangible are the 

 lessened black of the head, the greyer and less orange suffused 

 limbs (especially the thighs), and the restriction of the orange 

 of the feet to their edges, the whole of their upper surfaces 

 being uniform u orange-ochraceous " in the true IS. Oerstedi. 



Saccopteryx bilineata centralis, subsp. n. 



Similar in all essential respects to the true S. bilineata of 

 northern South America, but the size is rather less and the 

 build more delicate, as indicated by the skull. Colour as in 

 bilineata, but the dorsal lines usually more brownish white, so 

 that they do not contrast so conspicuously with the general 

 body-colour. 



Skull, as compared with that of true bilineata, smaller 

 (total length 15 - 5 mm. as against 17) and more lightly built. 

 Crests and ridges less developed, postorbital processes smaller 

 and weaker. Brain-case more inflated at its antero-external- 

 superior corners, the convexity markedly stronger and more 

 projecting than in the larger form. Teeth smaller throughout. 



Dimensions of the type (measured in spirit) : — 



Forearm 47 mm. 



* Arch. f. Nat. xxxv. p. 260 (I860). 



t The type locality of & Oerstedi is not, as stated by Miller and Eehn, 

 Cartago, Costa Rica, but Chiriqui, whence Oersted's specimen had been 

 brought alive to Cartago. The original figure and description agree 

 with Chiriqui specimens in all the characters distinguishing the latter 

 from the Costa Eican form. 



