144 MR. o. THOMAS OX THE [Feb. 20, 



Mammal discovered during Mr. Johnstou's exploration of the 

 Nyasa Fauna, I have named in his honour, is remarkable as being 

 the only member of the genus distinguished by any colour-markings 

 other than those of the dorsal spot. The prominent black ear- 

 mark is in fact quite unique in the group, while its reddish-brown 

 crown, although sometimes present in P. abyssiiiicct, will readily 

 distinguish it from its nearest ally, P. capensis, in which the crown 

 is finely grizzled like the back. The unusual massiveness oE the 

 grinding-teeth will also readily separate P. johnstoni from all other 

 forms. 



The occurrence of this peculiar but clearly representative species 

 between the ranges of P. cajiensis and P. shoana tends to confirm 

 their distinctness from each other, on which I had thro^vu some 

 doubt when writing in 1892, 



Since my monograph of the genus was prepared, two species 

 of Procavia have been described by Dr. Matschie \ but both 

 belong to the Dendro7ii/mx group, and have therefore nothing to 

 do with P. johnstoni. 



25. Pkocatia beucei. Gray. 



a, b. Ad. & imm. sks. $ . Mpimbi, Upper Shire. 4/93. 



c Tg. sk. Fort Lister, 3500 ft. 25/7/93. 



These specimens probably represent Hi/ra.v mossmnhiciis, Peters. 

 The youngest of them has already got its interparietal sutures 

 closed. 



The basal lengths of the three skulls are : — 



a. (Stage Vin.), 79 mm. ; b. (Stage V.), 71 ; c. (Stage IIT.), 63. 



The ears of these examples are more prominently white than 

 is usual in P. brucei, and their bellies and feet are also particularly 

 white, characters in which they somewhat resemble the closely 

 allied P. bocagei, and it is probable that when more specimens 

 of the latter are obtained the two forms will be found to grade 

 into one another. 



In looking at the fine set of Dassies from Nyasa now sent, 

 three of P. johnstoni and three of P. brucei, all found more or less 

 together, one cannot fail to be struck by the peculiar method in 

 which evolution seems to have been going on in the group. Not 

 only do they afford a striking instance of the remark made pre- 

 viously ^ as to the constant occurrence together of one species of 

 the hypsodont and one species of the brachyodout group, the com- 

 petition between members of the two groups apparently not being 

 severe enough to prevent their hving together, but also, the 

 practicability of their living together being once proved, they seem 

 then to have tried to become as different from each other in their 

 superficial characteristics as possible. Thus, while the hyposodont 

 P. johnstoni is distinguished from its allies of the same group by 

 its darh head, black ear-markings, dirty yelloiv belly, and black 



1 S.-B. nat. Fr. Berl. 1892, p. 110, and 1893, p. 112. 

 = P. Z. S. 1892, p. 57. 



