10 BULLETIN 99, UNITED STATES NATIONAL MUSEUM. 



and Heliosciurus is said to possess ''molars of typical Sciuims stmc- 

 ture." Later these three African species were removed by Thomas ^ 

 from Sciurus on the character of the l^aculum alone, and placed in a 

 5iew genus, Mthosciurus, further distinguished from Heliosciurus 

 by the presence of two upper premolars. 



Comparison of the teeth of Sciurus vulgaris with those of Helio- 

 sciurus and those of the African species referred to Sciurus (and later 

 to ^Ethosciurus) shows that all these African species are closely 

 related and that all differ considerably from true Sciurus. Speci- 

 mens of ^' jEtltosciurus" poensis and "J.'' ruwensoni agree in all essen- 

 tial details of dental structure with Heliosciurus, and these all differ 

 considerably from Sciurus vulgaris. The lower molars, both in 

 Heliosciurus and jEthosciurus, are more complex, with definite 

 transverse ridge across forward part of crown which isolates a narrow 

 valley anterior to the central basin. The transverse ridges of the 

 upper molars of Sciurus are nearly parallel, while in the African 

 species these ridges are strongly convergent on inner side, and there 

 is always present a slightly developed hypocone. These struc- 

 tural peculiarities of the molars are of so nnich more importance than 

 the presence or absence of a small spike-like upper premolar that it 

 is obvious the African species referred to Mthosciurus are in reality 

 closely related to Heliosciurus and well removed from Sciurus. The 

 two African .species of jEthosciurus that I have seen (I have not 

 seen A. lucifer) are closely related, as shown by their peculiar colora- 

 tion and the presence of the functional pin^, and should on this account 

 form a subgenus of Heliosciurus. In view of the very close rela- 

 tionship to true Heliosciurus and the fact that specimens of the 

 latter sometimes exhibit spike-like small upper premolars it would 

 hardly seem proper to recognize jEthosciurus as a full genus. 



For measurements of specimens of the squirrels of this genus, see 

 nage 13. 



^ ' HEUOSCIURUS RUWENZORU (Schwann.) 



1904. Scmrus rufobrachiat-us ruivenzorn Schwann, Ann. and Mag. Nat. Hist., 

 ser. 7, vol. 13, p. 71. Januaiy. (Wimi, or liuimi, Valley, Ruwenzori, 

 Uganda; type in British Museum.) 



1010. Sciurus ruwenzorii Thomas and Wroughton, Trans. Zool. Soc. London, 

 vol. 19, p. 497. March. 



Specimen. — One, from — 



Uganda: Mubuku Valley, Mount Ruwenzori (Carruthers). 



The members of the Ruwenzori Expedition found this squirrel 

 "plentiful on Ruwenzori from 6,500 feet up to 8,500 feet, the bounda- 

 ries of the forest-zone" ^ A geographical race has since been 

 described from Vulcan Forest, north of Lake Kivu.^ 



This species is a member of the subgenus jEthosciurus . 



> Ann. and Mag. Nat. Hist., ser. 8, vol. 17, p. 271. March, 1916. 



2 Thomas and Wroughton, Trans. Zool. Soc. London, vol. 19, p. 497, March, 1910. 



3 Sciurus nuvcmorii vulcavius Thomas, Ann. and Mag. Nat. Hist., ser. 8, vol. 4, p. 476, November, 1909. 



