244 On a new Sjjecies o/3kIyopus /»•(■??? Central Aisia. 



median spinous pioces?. Tl)e squamosals approach within 

 1"1 mm. of each otlier in the fore part oE the brain-case, and 

 tlie Li-sleplianic width is reduced to 3'9 mm.; in an equally 

 old skull of J/, schisiicolor these two dimensions are 2*3 and 

 4*7 mm. respectively; tliese differences indicate an increased 

 development of the anterior portions of the temporal muscles 

 which is doubtless correlated with the enlargement of the 

 molars. 



Cranial di7netis>ons. — Condylo-basal leupth 25'8 mm, ca. ; zygomatic, 

 breadth 16'o; interorbital constrictioc 3'1 ; mastoid breadth 12'6 ; length 

 and anterior width of nasals 7*o and 3; diastema 7"5; cheek-teeth 

 (alveolar) 7'8; palatal depth 9-4; cranial depth 8-3; mandible 16'7 ; 

 mandibular cheek-teeth (alveolar) 7"3. 



Remarks. — MiddendorfF (' Sibirische Reise/ ii. 2, p. 108) 

 long ago suspected that " Myodes schisticoJor " ranged right 

 across Northern Europe and Asia. He described a specimen 

 Irom Ajan on the west coast of the Sea of Okhotsk, "which 

 just as completely agrees with Lilljeborg\s descri|)tion and 

 figures as if it had sat as the model." This statement was 

 generally ignored until 1012, when HoUister * described his 

 M. niorulus, based upon a specimen which he collected in a 

 nut-pine forest, at an altitude of 6875 feet, near Ta])ucha, a 

 )ilace in the Altai IMountains 125 miles S.K. of Biisk. This 

 differs from M. schisiicolor in its darker more blafkish coloi'a- 

 tion ; duller and much more extensive rusty mantle ; laterally 

 com})ressed, rounder looped, and ratlier smaller cheek-teeth ; 

 and smaller and much flatter auditory bullfe. In every respect, 

 therefore, save in thecharacter ofthe mantle, M.moi-ulus\s\evy 

 different from the form before me. The hitter comes from a 

 point some COO miles to the east of the ly})e locality of 

 AJ. moruhis, and may be regarded as the most highly 

 s|)ecialized member of the genus yet discovered; this is 

 proved by the cranial and dental characters, which in seveial 

 important respects show an advance upon those of AI. schifiti- 

 colur in tiie direction of Lemmus, and by the lightening of 

 the colour, which causes the s])ecies to ])r('sent such a strong 

 suiterficial resemblance to L. uhensis that when Mr. Thomas 

 cursorily exatnined the ty[)e in the lirsl place he failed to 

 discover its true afrmities. 



* Pmith'ioniai) Misc. Coll. Ix., Nov. L'O, llil2, no. 11, p. 1 ; and Proc. 

 I'.S. Nat. Mus. xlv. \k 014 (L^Lst June, l<Jl3j. 



