516 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



VOL. 45. 



enamel pattern is present in 28. Two have m^ abnormal. In 

 one, No. 175333, the last loop has an additional inner reentrant 

 angle posteriorly; and another, No. 175325, has the second outer 

 salient angle of m ^ so reduced, and the first inner triangle so length- 

 ened transversely, that it has the appearance of a second loop, much 

 like the anterior loop. It seems quite certain that this is an inde- 

 pendent species, and not a race of Microtus arvalis. Poliakoff evi- 

 dently confused other forms with it. It is uncertam from his account 

 whether he considered the original example the Altai or the Kirgliiz 

 Steppe specimen, listed by him. Eversmann in his original descrip- 

 tion, however, mentions only the Altai and gives measurements of 

 only one specimen. 



Measurements of selected adult specimens of Microtus obscurus from the Altai Mountains, 



Siberia. 



Locality. 



Tchegan-Burgazi Pass 



Do 



Do 



Do 



Tapucha 



Do 



Do 



Do 



D6 



Do 



Do 



Do 



Do 



Do 



Do 



Do 



Do 



Do 



mm. 

 5.9 

 6.1 

 6 



6.3 

 6.1 

 5 



5.7 

 6.1 

 5.1 

 6 



5.8 

 6 

 6 



5.8 

 5.9 

 6.1 

 6 

 6.4 



MICROTUS (STENOCRANIUS) EVERSMANNII (Poliakofi). 



1881. Arvicola eversmannii Poliakoff, Annex. Mem. Acad. St.-Petersbourg, vol. 



39, p. 285. 

 1901. Microtus (Stenocranius) eversmanni K.a.stschenko, Ann. Mus. Zool. Acad. 



St.-P^tersbourg, vol. 6, p. 186. 



Eight specimens from the heavy pine forests near Tapucha are 

 referred to this species, described from the Altai. The skins in this 

 series are readily distinguishable from specimens of tianschanicus 

 from the desert ranges to the southward by their richer, darker color, 

 above and below. There seem to be no diflterences in external 

 measurements nor in the skulls and teeth of the two forms and they 

 probably intergrade. There is a great variation in the size of skull 

 in both forms. Skulls of adults in the Tapucha series range from 25 

 to 27.5 mm. in condylobasal length. There is a strong tendency 



