﻿52 



NORTH AMERICAN FAUNA. 



[No. 12. 



Subgenus ALTICOLA Blanford. 



1884. AlticoJa Blanford, Jouru. xisiat. Soc. Bengal, L, Pt. II, p. 89, 1884. Type 

 Arvicola stoliczl-cunis Blanford. 



Geographic distrihtition of type species, — ''Higii plateaus of i^'ortliern 

 Ladak (\Yesteru Tibet)" (Blanford). 



OeograpMc distribution of subgenus. — Boreal Zone iu the Himalayas. 

 Essential characters : 



Palate abnormal. 



m 3 without closed triangles. 



m 1 with 4 or 5 closed triangles and 7 salient angles. 



m 3 normally with 2 closed triangles and 5 or 6 salient angles; posterior loop 

 produced backward in line of jaw. 

 Mammae, 8. 

 Plantar tubercles, 6. 

 Sole, hairy. 



Claws on hind feet longest. 



Fur long and soft but not highly modified. 



Skull. — The skull in this subgenus (PI. I, fig. 10) shows no striking 

 peculiarities to distinguish it from that of true Microtus. The general 

 shape is usually much as in Microtus arvalis, 

 ^^^^^^ but the zygomatic arches are more flaring and 

 -^IXhTLAA brain case is somewhat broader and flatter. 



The rostrum is proportionally longer than in 

 Fia.26.-Enam8i pattern of mo- Micvotus proper, aud the audital bullae (fig. 27) 

 lar teeth, Microtus ^Aiticoia) are morc inflated and papery. 

 aiucaudaitjv^). (x 5.) Bomj paJatc—Th^ median palatal ridge (PI. 



II, fig. 4) widens at a point opposite the space between the second and 

 third molars and is approached, as in the typical microtine palate, by 

 outgrowths from the opposite sides of the lateral grooves. These out- 

 growths, however, do not meet the median ridge, but leave the lateral 

 grooves open. Just at its widest point the median ridge is squarely 

 truncated. The sloping terminal ridge is entirely lacking and the space 

 that it usually occupies forms the anterior end of the very long rectang- 

 ular interpterygoid fossa. A structure of much the same appearance 

 could be produced by widening the anterior end of such a hastate 

 interpterygoid fossa as that often i^resent in ^Aulacomys^ (PI. II, fig. 7) 

 until the whole space acquired an equal breadth. The floors and median 

 walls of the lateral pits would then be so encroached upon as to oblit- 

 erate the pits, while a few slight further modifications would give a 

 l>alate indistinguishable from that of Alticola. The palate of Alticola 

 resembles that of JS^eofher more closely than it does that of any other 

 subgenera except Syperacrius. 



Enamel pattern in general. — The enamel pattern in Alticola (fig. 26) 

 differs in many ways from that of any subgenus of Microtus. In gen- 

 eral it is characterized b}^ ('^O ^ tendency to reduction in the number of 

 prisms in the variable teeth; (&) by a i)eculiar irregularity and indefi- 

 niteness in outline j (c) by a strong tendency toward bilateral symmetry 



