1900.] MAMMALS FROM SOUTHERN ABYSSINIA.. 81 



8. ARVICANTHIS DEMBEENSIS. 



$ . Kombolsha, 16th February, 1899. 



"Shot close to water-side among reeds. Small colony ; native 

 name 'Ait'." 



Measurements taken in the flesh — head and body 113 millim., 

 tail 105, hind foot 26, ear 17. 



This species, described by Riippell in 1812, is represented in the 

 British Museum by only a single specimen obtained by Dr. W. 

 T. Blanford while accompanying Lord Napier's expedition to 

 Magdala. The fur of this species is much softer and the aunu- 

 lations finer that in A. abijssinicus, and the belly is almost entirely 

 white. The skull is rather less angular, and the palatal foramina 

 are shorter, not reaching so far back as the first molar. The molars 

 of the two species (see figs. A & B) are strikingly different ; the 

 first upper molar of A. dembeensis is oval in shape, having only 

 7 cusps (the 8th being vestigial), three in the middle line with 

 two inner and two outer of almost equal size placed in the 

 intermediate spaces, so that the tooth is almost rose-shaped, six of 

 the cusps surrounding the central one. It will be seen that the 

 usual third outer cusp is almost entirely wanting. 



A 



A. Right upper molar series of Arvicanthis abi/ssinicus. 



B. Right upper molar series of A. dembeensis. 



The second upper molar is formed of six cusps, two larger in the 

 middle line and four smaller — two outer and two inner — set in 

 advance of the larger pair, so that the front of the tooth is concave, 

 and the hind part convex, being formed of the middle cusp only. 

 The pattern formed by the cusps of these two molars is very sym- 

 metrical, with the row of five large cusps of equal size in the middle 

 line, and four smaller cusps on either side placed in the intermediate 

 spaces. 



The last molar is quite one-sided, being formed of one large 

 cusp, in a straight line with the large middle line of cusps in the 

 other teeth, and three smaller ones, all on the inner side, the hinder- 

 most forming the posterior border of the tooth. 



The drawings (A & B) will more readily explain the formation 

 of the teeth of these two species. 



9. Arvicanthis abyssinicus. 



2. Laga Ilardim, loth January, 1899. 

 2 . Jiffa Densa, 7800 ft., 23rd' January, 1899. 

 Proc. Zool. Sou— 1900, No. VI. 6 



