﻿70 



NORTH AMERICAN FAUNA, 



[No. 12. 



GeograpJiical distribution of snhgemis. — The rauge of the subgenus 

 Keofiher is the same as that of the tyi^e and only known sjoecies. 

 Essential characters : 



Palate abuormal. 



m 3 with all triangles closed. 



m 1 with 5 closed triangles and 9 salient angles. 



m 3 with 2 closed triangles and 6 salient angles. 



Mamiuie 4. 



Plantar tnbercles 5. 



Sole naked. 



Claws on hind feet longest. 

 Fur highly modified. 



SMIL — The skull of JS'eoJiher is cliaracterized by its large size, great 

 depth through the frontal region, and conspicuous development of 

 postorbital processes. The ratio of fronto-palatal depth to basilar 

 lengtli is about 41 in Xeofiher^ while in true Microtus it is only about 

 35. As the occiput in Neofiler is not correspondingly liigli the dorsal 

 outline of the skull curves gently and regularly from front to back, 

 with the highest point just behind the orbits. When viewed from 



above the skull of Neofiher differs from that 

 of Microtiis chietly in the larger squamosals, 

 smaller parietals and interparietal, and in 

 the sharp-pointed postorbital processes. 

 The latter project over the orbital cavity 

 as square- cornered shelves, which are espe- 



FlG. 36.— Enamel pattern of molar Cially UOticeable whCU vicWCd from bclOW. 



teeth, Microtus (Neofiher) aiieni. PaUtc—ThQ bouy palate in Kcofiher (PI. 



II, iig. 9) differs Avidely from that of Microtus j 

 and exactly resembles that of Fiber (p. 72). 



Enamel pattern in general. — In general the enamel pattern of Xeo- 

 fiber (fig. 36) is characterized by a tendency to reduction in the number 

 of angles in the variable teeth and to the tight closure of all triangles. 

 The latter peculiarity gives the teeth the greatest possible strength. 



Front lotver molar. — The first molar in the lower jaw exactly resem- 

 bles the corresponding tooth in Microtus excei^t that the anterior loop 

 is rather shorter than in the typical members of that subgenus. In 

 one specimen (^^o. 23453, U. S. !N"at. Mus.) the anterior loop has two 

 indentations on the outer side, thus suggesting Anaptogonia. 



Baclc upper molar. — The third maxillary tooth is like that in the 

 subgenera Fitymys, Fedomys^ Fhaiomys, ChUotMs, and typical Arvicola, 

 as it has only two closed triangles and six salient angles. 



Other teeth. — The back lower molar has all the triangles tightly closed, 

 in this respect differing from all other subgenera exceiot Lagurus. 

 Closed triangles are sometimes formed in the third lower molar of 

 almost any of the larger voles, but Keofiber and Lagurus are the only 

 groups in which they are always present. Outside the subgenus 

 Lagurus^ most of the known species of which are small, the tendency to 



