374 MICROTIN^ 



below, and therefore before the growth of the crown can be said 

 to be completed. 



5. t Mimomys pusillus Mehely. 

 1914. Microlomys pusillus Mehely, Ann. Mus. Nat. Hungar., 12, p. 214. 



Ledotype. — No type being indicated in the original description 

 I now select the young left mandibular ramus, of which the cheek- 

 teeth are figured by Mehely in his Taf. vii, fig. 8, as the lectotype 

 of this species. 



Type horizon and locality. — Bone breccia of the Somlyo-Berg, 

 Piispokfiirdd, Hungary; Late Pliocene ('" erste interglaziale 

 Periode " of Mehely). 



Range in time and space. — Known only from the type horizon 

 and locality. 



Characters. — Closely resembling M. intermedius in the enamel 

 pattern of its molars, but distinguished by its more reduced m' 

 and its smaller size, which does not exceed that of Microtus 

 arvalis. 



Skull known only from a palatal fragment, figured by Mehely 

 {op. cit., Taf. vii, fig. 1). In this the posterior-lateral bridges are 

 situated a little further forwards than in M. intermedius, and 

 the posterior median sloping septum is distinctly longer and 

 rather narrower. The maxillo-palatine suture extends forwards 

 to a point opposite the fore-part of m^ instead of ending opposite 

 the middle of that tooth, and there is no trace of a median 

 suture. 



Cheek-teeth. — Re-entrant folds partly filled with cement; 

 m^ and w^ of normal pattern; m^ with two roots, of which the 

 anterior is the larger and consists of two completely fused though 

 clearly recognizable elements ; m^ with three outer and three inner 

 salient angles, the third inner angle much less developed than in 

 M. intermedius ; outer infolds shallower than in the latter species, 

 the first triangle more or less confluent with the anterior loop 

 as in Alticola, etc., though substantially shut off behind from the 

 posterior triangles, which are more or less broadly confluent with 

 each other and with the posterior loop. In adult stages of wear 

 typical examples of the ?«j are exactly like adult specimens of 

 the H?j of M. intermedius in form. In young stages the third 

 outer salient angle usually bears a well-marked prism-fold; in 

 front of this, in one example figured by Mehely (Taf. vii, fig. 

 13), there is an ephemeral enamel islet, showing that the third 

 outer valley is reduced by insulation of its inner portion exactly 

 as in M. intermedius. The " prism-fold " usually disappears com- 

 pletely before the tooth shows any sign of rooting; as Mehely's 

 fig. 12 indicates it occasionally persists in specimens with well- 

 developed roots, but it always dies out at some distance above the 

 base of the crown, instead of being perfectly persistent as in 



