Lint of tlie Rodents of South Africa. 233 



much elongated but not well developed, all the toes clawed, the first 

 short and not reaching the base of the second. 



Tail a little shorter than the head and body, cylindrical, covered 

 with scales, which, however, are concealed by the long black hairs, 

 these are about '25 in. long towards the base, but gradually increase 

 to about -75 in. at the tip, the extreme base of the tail is the same 

 colour as the body, the rest of it is black. 



Incisors yellowish. 



Dimensions (from a specimen in alcohol). Head and body 5 '75 ; 

 tail 5'30; hind foot 1-25; from ear-opening to tip of nose 1*50; 

 length of a skin according to Smith 7 '25 ; skull length 1-63, breadth 

 98 ; upper molars -38. 



Distribution. The Eock Eat has been found only in Namaqualand ; 

 Sir A. Smith obtained his specimens in the mountains towards the 

 mouth of the Orange Eiver. The South African Museum is indebted 

 to Dr. Howard for examples of this species, obtained at Klipfontein 

 about fifty miles inland from Port Nolloth. 



GEN. THEYONOMYS. 



Aulacochis, TEMMINCK, Monogr. Mam., i., p. 245 (1827) (nee 

 Eschschricht). Type T. swinderenianus. 



Thryonomys, FITZINGEB, S. B. Akad. Wien, Ivi., p. 141 (1867). 

 Type T. semipalmatus. 



Stout, rat-like animals, with blunt muzzles, harsh fur, and short 

 tails sparsely covered with stiff bristles ; the fore feet with a 

 rudimentary pollex and a small fifth toe, the hind foot with only 

 four digits, the outer (fifth) being very short. 



Skull with inflated facial and small cranial divisions, the occipital 

 and lamboidal crests are very well developed, the antorbital opening 

 is large and has a special basal groove for the reception of the 

 nerve. 



Dentition. i. 1/1; c. 0/0 ; p.m. 1/1 ; m. 3/3 = 20; incisors very 

 broad, the upper ones with three strong longitudinal grooves ; the 

 lower ones smooth ; molars rooted, with, in the upper jaw two 

 external and one internal enamel folds ; in the lower jaw one 

 external and two internal folds. 



The use of the old and more familiar name for this genus, 

 Aidacodus, has recently been shown by Thomas to be inadmis- 

 sible, as it was previously used by Eschschricht for a genus of 

 Coleoptera. 



