328 MICROTIN^ 



Skull (Fig. 92) delicately built, broad, remarkably depressed, 

 and presenting a very unusual appearance in profile. The dorsal 

 contour is gently convex along the rostrum, where it is nearly 

 parallel with the curve of the diastema, slightly concave in the 

 interorbital region, and thence very slightly convex along the 

 braincase to the gently shelving occiput. Owing to the depression 

 of the upper surface, the frontals rise very little above the zygo- 

 mata. Rostrum and zygomata slender and delicate. Zygomata 

 diverging posteriorly; jugals very light. Nasals ending in front 

 about flush with the anterior surfaces of the incisors, terminating 

 behind very slightly in advance of the front margins of the orbits. 

 Interorbital region unusually broad, slightly concave from before 

 backwards as well as transversely. Temporal ridges well marked 

 in adults, although widely separated in the interorbital region and 

 throughout. Squamosals showing some tendency to encroach 

 upon frontals anteriorly, with well-developed post-orbital crests, 

 and large supratympanic fenestrse. Interparietal large and normal. 

 Infraorbital canal essentially as in other voles, but its upper 

 part rather wider, its inferior slit-like portion lower and broader, 

 and its outer wall rather narrower than usual. Anterior palatal 

 foramina large, reaching back almost to the molar region. Palate 

 essentially as in Alticola ; but the slender postero-lateral bridges 

 are usually complete and the post-palatal pits and choanse are 

 shallower than usual. Pterygoid fossae large but shallow, their 

 floors scarcely dorsal to the ventral surface of the basisphenoid. 

 Ectopterygoid plates low, forming an unusually obtuse angle with 

 the alveolar borders of the maxillse. Auditory bullfe simple as in 

 Alticola, rather large though not greatly inflated, the parts around 

 the eustachian tube forming a long pointed process. Mandible 

 very slender, with long slender processes; angular process with 

 its lower border thickened throughout for insertion of anterior 

 portion of masseter lateralis muscle. 



Dentition throughout light and weak. Upper incisors strongly 

 curved, slightly opisthodont. Lower incisor displaces m^ in the 

 normal way, but terminates in the base of the condylar process 

 below the dental foramen. Cheek-teeth (Fig. 91, figs, za, zb) 

 persistently growing, with a little cement in the re-entrant folds. 

 Enamel pattern as in Alticola, the peculiar stretched-out appear- 

 ance of the teeth very noticeable in adults, less so in adolescent 

 specimens ; in^ much simplified with three salient angles on each 

 side, the first outer triangle small and broadly confluent with the 

 anterior loop. 



For external and cranial measurements, see tables at end of 

 volume. 



Remarks. — Nine specimens of this interesting vole, viz., 

 one presented by Mr. G. H. Miller in 1908, and eight received from 

 Prof. Sushkin in 1923, are now available. They were collected 

 at various points on the Altai Mountains at elevations between 

 1000 metres and 8500 feet. Making due allowance for differences 



