﻿56 



NORTH AMERICAN FAUNA. 



[No. 12. 



lu 1 normally witli 3 closed triangles and 8 or 9 salient angles, 

 ni 3 normally witli 2 closed triangles and 6 salient angles. 

 Mammae 4. 

 Plantar tubercles 5. 



Sole thickly liaired between lieel and tnbercles. 

 Claws moderate in length, those on hind foot longest. 

 Fur not specially modified. 



Sl'ulL — The skull of Microtus ausferuSj the only known sjiecies of 

 PedomySj is remarkable for the subcylindric brain case, and great depth 

 of all that part back of the rostrum. While the skull of Fedomyn is not 

 strikingly difl'erent from that of true Microtus it is very unlike the 

 flattened skulls of Phaiomys, Pitymys^ and Gliilotus^ the other grouj^s of 

 small voles resembling Pedomys in tooth characters and in number of 

 mammas and footpads. 



Bony palate. — The bony palate is typical, though the interj^terygoid 

 fossa is seldom squarely truucate anteriorly. 



Enamel pattern in general. — The enamel pattern (fig. 29) is charac- 

 terized by simplification in the structure of the variable teeth. 



Front lower molar. — The first mandibular molar has a i^osterior trans- 

 verse looi3 followed by three closed triangles and an anterior loop. 



The anterior loop is deeply indented by two 

 reentrant angles, one on each side. These 

 sometimes cut deep enough to isolate a fourth 

 or even a fifth closed triangle, but this rarely 

 takes i)lace. There is often a very faintly de- 

 FiG. 29.— Enamel pattern of mo- vclopcd reentrant auglc close to each side of 

 ^'T !r!l^' ^'r'''' ^^'"'""'^'^ the tip of the anterior loop. In cases where 

 these are strongly marked a front tooth pre- 

 cisely resembling that of Microtus is the result. 



Bacli upper molar. — The posterior maxillary tooth is exactly like that 

 of ISfeofiher, Pity my s., Phaiomys, Chilotus^ and tyx)ical Arvicola, having 

 an anterior transverse loop, two closed triangles and a short posterior 

 loop, from the outer base of which a third closed triangle may souie- 

 times be cut. 



Other teeth. — With the exception of the two teeth just described, the 

 dentition of Pedomys is like that of the tetramerodont species of the 

 subgenus Microtus. 



Mamma'. — There are four mammie, all inguinal. 



Feet. — Soles densely hairy between heel and tubercles; pads five, 

 with no indication of a rudimentary sixth. 



General remarlcs. — Pedomys agrees in tooth pattern Avith Pity my 

 ChilotuSj and Phaumys, but differs from all three in tlie shape of the 

 skull, and from the last in the short claws and unmodified fur also. 



Subgenus PHAIOMYS Blyth. 



1863. Phaiomys Blyth, Journ. Asiat. Soc. Bengal, XXXII, p. 89, 1863. Type Fhaiomys 

 leuciirus Blyth=AIicrotus hli/thi Blandford. 



'A skull of Microtus rattlceps from Norway exactly resembles skulls of M. austerus 

 except that the rostrum is more slender. 



