110 Mr. 0. Thomas on new 



Incisors enormously thick and large, far heavier than in 

 any other member of the group. Cheek-teeth three in number 

 above and below, as in glaber^hwt very small, as in phillipsi ; 

 the posterior one much the smallest. 



Dimensions of the type (very old), measured in the 

 flesh :— 



Head and body 115 mm. ; tail 35 ; hind foot 18. 



Skull: condylo-basal length 23 ; condyle to incisor-tip 26 ; 

 greatest breadth 18"5 ; nasals 7"5 x5 ; intertemporal breadth 

 5*5; greatest mastoid breadth 12*5; combined breadth of 

 upper incisors 3*0; diastema 7'7 ; palatilar length 11*3 ; 

 length of upper tooth-series 29. 



Uab. Wardairi, Central Somaliland. 



Type. Aged female. B.M. no. 4. 5. 9. 23. Original 

 number 141. Collected 31 January, 1904, and presented by 

 Maj. H. N. Dunn, R.A.M.C. 



This species is based on the specimen referred in 1904*, 

 with great doubt, to Fornarina philhpsi, of which it was 

 thouglit it might be a very old individual, with the incisors 

 enormously developed, and three cheek-teeth present — either 

 as an abnormality or the last tooth erupted in old age. But 

 additional specimens of //. glaber, immature and old, since 

 received from Dr. Drake-Brockman, show that no such 

 development of the incisors occurs in old age in that animal, 

 and 1 am now convinced that the present form is quite 

 distinct. 



H. dunni is of special interest, as with the dental formula 

 of Ileterocepkalus glaher it has the low coronoid process and 

 small-sized cheek-teeth of Fornarina phillipsi^ and is therefore 

 intermediate between the two. Younger specimens will, 

 however, be needed before a decided opinion can be expressed 

 as to its general position and the bearing its characters have 

 on the distinction of Fornarina from Heterocephalus. 



I may take this opportunity to express an opinion about 

 the homologies of the teeth of Heterocephalus and the allied 

 genera forming the family Bathyergidse, a matter of great 

 interest, but of extreme difficulty, owing to the way in which 

 the teeth succeed each otiier, and their resemblance inter se^ 

 so that homologization by form is not possible. 



The key to the situation is clearly the genus HeUophohius^ 

 in which the full dentition consists of no less than six teeth, 

 I. e. P. 2 . 3 . 4, M. 1 . 2 . 3. All six are, however, almost 



* Ann. & Mag. Nat. Hist. (7) xiv. p. 104 (1904). 



