288 PROCEEDINGS OF THE ACADEMY OF [1899. 



appearance it strongly suggests an approach to Phaiomys. This is 

 due chiefly to the protruding upper incisors and the short, strongly 

 cuueate nasals. The whole skull is angular and heavily built, 

 much broader than that of M. arvalis, from Germany, though of 

 about the same length. Nasals shorter than in 3f. arvalis, and 

 much broader anteriorly. Zygomatic arches strongly flaring ante- 

 riorly, nearly parallel in region opposite postorbital processes. 

 Interparietal rectangular, the anteroposterior breadth about half 

 the lateral breadth. Braincase squarish in outline, broader than 

 in M. arvalis, but of about the same depth. luterorbital constric- 

 tion relatively less narrow than in Jf. arvalis, but constricted region 

 of about the same length. Palate normal, the lateral pits well 

 developed, though shallower than in 31. arvalis. Audital bullte 

 about the same size as in 31. arvalis, but flatter. Incisive foramen 

 considerably broader anteriorly than posteriorly. 



Measurements of type skull : greatest length, 25 ; basal length, 

 14.6; basilar length, 14; zygomatic breadth, 16; mastoid breadth, 

 12.4; interorbital constriction, 3.8; length of nasals, 7; anterior 

 breadth across nasals, 3.6; posterior breadth across nasals, 1; 

 diastema, 8.8; palatal length, 14.4; occipital dejith, 8; fronto- 

 palatal depth (at middle of molar series), 8; mandible, 17; maxil- 

 lary toothrow (alveoli), 6.8; mandibular toothrow (alveoli), 6.6. 



Teeth. — Attention has already been called to the strongly pro- 

 jecting upper incisors. The molars are heavier than in 31. arvalis. 

 In general appearance the enamel pattern is less compact than in 

 31. arvalis, while the details in the two species differ considerably. 

 The posterior upper molar contains an anterior transverse loop, 

 a small outer closed triangle, a larger one on the inner side, and 

 a long terminal longitudinal loop provided with a well-developed 

 salient angle on each side anteriorly. Behind each of these salient 

 angles is a rounded reentrant angle. As the inner of these saHent 

 angles and its corresponding reentrant angle are the more strongly 

 developed as well as the more posterior in position the terminal 

 loop is bowed very slightly inward. It is, however, essentially 

 straight as compared with the corresponding region in 31. arvalis. 

 Middle upper molar tetramerodont. The front lower molar con- 

 tains the same elements as in 3f. arvalis, but the two anterior 

 triangles open freely into the terminal loop. This character may 

 prove to be individual, though I am inclined to believe that it is 



