46 EINAR LÖNNBERG, MAMMALS COLLECTED IN CENTRAL AFRICA. 



widely from these two species. As P. batesi is described as »rufous almost red-mahogany » 

 it is also very different in colour. In a specimen from Mukimbungu, Lower Congo, which 

 I regard to be P. batesi, the bristle hairs are black, unlike those in the new species. 

 P. jaustus which Thomas has originally described 1 from »Irneti Bompona, R. Maringa, 

 Central Congo» and quite recently 2 also mentioned from Medje and Poko, Upper Congo, 

 is also provided with a very short tail, »shorter than nsual», viz. 38 mm. With regard to 

 the colour P. jaustus reminds about the present species by the presence of a »large number 

 of hoary-tipped hairs intermingled with the general for on the body behind the shoulders » 

 — . »Of the thin outer hairs projecting beyond the wool-hairs perhaps half are 

 blackish and half hoary-tipped. » This partial resemblance cannot, however, lead to 

 identif ication with this Potto from Masisi as the molars of both species are so widely differ- 

 ent. Thomas writes regarding P. jaustus about this: »anterior molar (m 1 ) smaller than 

 m 2 ; m 3 unusually large, little smaller than m 2 and fully as large as ra 1 . Small lower 

 premolars low, not exceeding m 1 in height» - — . In Arrhenius's Potto ra 1 is a little 

 smaller than ra 2 , but much larger than m 3 (ef. below), and small lower premolars 

 plainly exceeding ra x in height. 



Dimensions of Arrhenius's Potto: Head and body (skin) 395 mm; tail 70 mm; 

 hind foot 76 mm. 



Skull: 



Upper length, occiput to tip of nasals 62,8 mm. 



Basal length , 60 » 



Condyloincisive length 64 » 



Least interorbital width 10 » 



Zygomatic breadth 45,6 » 



Length of nasals (uncertain, suture obsolete) 16 » 



Palate length 25,3 » 



Breadth of brain-case 31,5 » 



Upper cheek teeth series 18 » 



Molars only 9 » 



Transverse diameter of m 1 3,7 » 



» » » m 2 3,8 » 



t> » » m 3 3,2 » 



The length of ra 1 and m 2 is practically the same or about 3,5 mm., but the inner heel 

 of ra 1 is a little narrower than that of ra 2 . The length of m* is about 2,3 mm. 



Length of lover jaw 45 mm. 



Lower series of cheek-teeth 15,5 » 



Molars only 10 » 



The formula of m 3 should thus be for this species 2,3 X 3,2, while it is for P. jaustus 

 3,4 x 4,7 according to Thomas (1. c. p. 427). 



De Winton has not published any cranial measurements of his P. batesi, and the 

 figures quoted by Elliot for the type of this species are unfortunately very uncertain 



1 Ann. & Mag. Hist., Sor. 8, Vol. VI^p. 426—427, 1010. 



2 » »> » » » » » XVI p. 467, 1915. 



