MICROTUS 



705 



(about concolor with flanks), the belly irregularly clouded by 



the slaty bases of the hairs. 



Skull. — The skull, though heavier and more massive than in 



any of the European members of the M. arvalis, has much the 



same general outline as in typical arvalis. The brain-case is, 



however, relatively deeper anteri- 

 orly, so that the dorsal profile is 



convex throughout (though much 



less so than in the Spanish 31. cah- 



rerse). Interorbital region with 



slight median longitudinal groove 



and low lateral ridges which do not 



tend to become united in any of 



the four skulls examined. Nasals 



strongly tapering posteriorly as in 



31. arvalis, their termination a little 



emarginate and slightly exceeded 



by nasal branches of pre-maxil- 



laries. Palatal foramina narrow, as 



in M. arvalis. Auditory bullae not 



peculiar in form, their size relatively 



somewhat greater than in 31. arvalis. 

 Teeth. — While preserving the 



typical arvalis pattern, the teeth 



are peculiar in a certain disjointed 



appearance of the prisms, due to 



the great depth of the re-entrant angles. The triangles are 



rather narrower in proportion to their width than in the other 

 members of the arvalis group, and the dentine 

 spaces have the appearance of being reduced 

 in proportion to the thickness of the enamel, 

 a character difficult to define but readily 

 appreciable to the eye. Except for these 

 general peculiarities the molars closely agree 

 with those of M. arvalis. First lower molar 

 with normal anterior loop, the outer re- 

 entrant angle well developed and approxi- 

 mately as deep as inner angle. Posterior 

 upper molar with the same elements as in 

 31. arvalis. 

 FIG. 144. 3Ieasurements. — External measurements of 



Mkruius hartiniji. X 10. type (adult male): head and body, 107; tail, 

 26 ; hind foot, 18. A second adult male from 



the type locality: head and body, 115; tail, 27; hind foot, J 8^; 



ear from meatus, 10. For cranial measurements see Table, p. 707. 

 Specimens examincd.—'Eight, all from the type locality. 



Bemarks. — Though very difierent from the other European 

 species of 3Iicrotus, this animal is nearly related to M. guentheri 



2 z 



Fig. 143. 

 .Uicrotus hartingi. Nat. size. 



