INTERRELATIONSHIPS OF GENERA 



87 



curvature of the tooth and its root is an exaggeration or accentua- 

 tion of the gentle backward curvature of the m^ seen in nearly 

 all voles ; in those in which the teeth have acquired the power of 

 persistent growth the curvature becomes marked and it is one of 

 the means of keeping the teeth " keyed " together tightly at the 

 grinding surface; but what the mechanical significance of this 

 character is in Prometkeomys and Ellobius I am not prepared at 

 present to say. That it is a character indicating, like others, a 

 special relationship between the two genera, I do not doubt; 

 it may be a character of accommodation, the m^ having come 

 into relation with the shaft of the incisor at a different moment in 

 its developmental history from that in which these two teeth have 

 come into relation with each other in other voles. 



" Bramus barbarus " Pomel,^ from the Quaternary Phosphorites 



I 



Fig. 56. — Cheek-teeth of Ellobius talpinus Pallas. 



Crown views : a. left upper, b. right lower molars lettered according 

 to the homologies of the cusps. 



of Tunis, is a most interesting fossil form known to science only 

 from the original description. Miller,^ in 1896, thought it " prob- 

 able that Bramus is the type of a group differing too widely from 

 any of the recent Microtince to be united with them in one sub- 

 family; " but in 1918 Miller and Gidley ^ placed the genus in the 

 family Rhizomyidsp, forming for it a special subfamily Bramince. 

 After carefully studying Pomel's most lucid though unfortunately 

 unillustrated account of the fossil species, I have come to the 

 conclusion that Bramus must be regarded as a synonym of Ellobius. 

 Every detail mentioned by Pomel, namely, the form of the molars, 

 the characters of their roots, the relation of m^ to the shaft of the 

 lower incisor, the form of the mandibular angle, the character 

 of the infraorbital foramen and the form of the interorbital region, 

 appears to be exactly as in Ellobius. The occurrence of this 



1 Pomel, Comptes Rendus, Paris, 114, p. 1159, 1892. 



« MuxEE, N. Amer. Fauna, No. 12, p. 74, 1896. 



3 MiLLEE and Gidley, Journ. Washington Acad. Sei., 8, p. 438, 1018. 



