758 RODENTIA 



middle, the posteroexternal border shortest, the inner border 

 nearly as long as anterior ; enamel extending over entire anterior 

 border and outer fourth of inner border. Lower incisors slender, 

 their roots extending well into bases of articular processes but 

 not forming noticeable protuberances on outer surface of man- 

 dible ; cross section of shaft differing from that of upper tooth 

 in the more triangular general outline and 

 relatively shorter, strongly convex anterior 

 border. Molars so like those of Microtus 

 arvalis that aside from the peculiarities of 

 the first mandibular tooth there is nothing to 

 distinguish with certainty between the two 

 patterns. Crown of third upper molar distinctly 

 longer than that of second. In Pitymys sub- 

 terraneus there is, however, a tendency for the 

 re-entrant angles to be wider and the closed 

 triangles relatively smaller, while the pattern of 

 nS^Euamei" ™ 3 appears to be more subject to distortion, 

 pattern, x 5. First outer triangle of ro 3 not infrequently 

 opening into inner triangle, but its apex always 

 on level with that of anterior loop and second triangle. Second 

 upper molar strictly as in M. arvalis. First lower molar 

 like that of Microtus arvalis except that third inner re-entrant 

 angle fails to penetrate to enamel wall of opposite side of tooth, 

 thus having a broad area of communication between first inner 

 and first outer triangles ; no exception to this condition has 

 come under my observation. 



BemarJcs. — Although bearing a strong superficial resemblance 

 to Microtus arvalis, and more particularly to the Alpine M. 

 incertus, this species is distinguishable externally by its rather 

 smaller ears, and by the number of mammae and plantar tubercles. 

 In colour it is usually a clearer, less yellowish brown than the 

 smaller forms of Microtus. Old and faded museum specimens are 

 often impossible to determine with certainty. The skull is 

 recognizable by its small size, nearly flat dorsal profile, wide 

 interorbital region, and by the almost perpendicular upper 

 incisors. Two geographical forms are known. 



Pitymys subteeeaneus subteeeaneus de Selys-Longchamps. 



1836. Arvicola subterraneus de Selys-Longchamps, Essai Monographique 

 sur les Oampagnols des environs de Liege, p. 10 (Waremme, Liege, 

 Belgium). 



1845. H[ypudmus] rufescente-fuscus Schinz, Synopsis Mamm., n, p. 240 

 (Urserenthal, Uri, Switzerland). See Mottaz, Bull. Soo. Zool. de 

 France, xx, p. 27, September, 1907. 



1845. Hlypudmus] rufofuscus Schinz, Synopsis Mamm., n, p. 240 (synomym 

 of rufescente-fuscus). 



1857. Arvicola subterraneus Blasius, Saugethiere DeutschJands, p. 388. 



