Douglass : Vertebrates from Montana Tkr tiary. 187 



In one specimen the posterior inner root of (lni.j is still preserved in 

 place. 



It appears, then, that the young of Myiagau/i/s has two milk molars. 

 If all described below belong to Myiagaiili/s at a certain stage during 

 the life of the animal, there are two milk molars and two permanent 

 molars ; while in some cases in old age there is only one tooth to take 

 the place of all these — a large premolar. Thus it is not improbable 

 that some individuals which had twenty teeth at one time of life were 

 finally reduced to four. 



The molar that is wanting in the adult animal is apparently the 

 first, as there is no evidence of the loss of M.j. The development of 

 the first molar is evidently prevented by the large, permanent pre- 

 molar. Perhaps under favorable conditions rudiments of My might 

 be found. 



Mylagaulus ? PRiSTiNus sp. nov. 



No. 742. Fig. 26. 



Mandible robust. Anterior and posterior angles widely separated, 

 the former extending far below the lower border of the horizontal 

 ramus and rounded, the latter oblique, high and projecting laterally 

 far outward. Permanent premolar large, very high, and with short 

 roots. The fourth temporary molar, which is retained in the present 

 specimen, is short, low, and has long roots. Molars -^ and -^ are of 

 moderate size and hypsodont. The enamel inflections and lakes on 

 the last temporary premolar and the two molars are either antero- 

 posterior or oblique. 



The large permanent premolar, though quite young, is somewhat 

 worn on the grinding surface. It has six enamel inflections, most of 

 which are oblique. To ascertain the form of the enamel pattern far- 

 ther down, the tooth was sawn in two about half way from the top of 

 the crown to the root. Here, as shown in Fig. 26, c, the pattern is 

 exactly that of Mylagaulus. There are five approximately longi- 

 tudinal lakes in three rows, as in M. paniensis. 



Mtv is nearly worn out. It is closely crowded against the premolar, 

 and on the anterior portion next to this tooth the enamel is absent. 

 Like the corresponding tooth in specimen No. 723, to be described 

 later, it looks as if the anterior portion of the tooth has been absorbed. 

 If the animal had lived the tooth would evidently soon have 

 been shed. Mj- is prismatic and quite high though its lower portion 

 cannot be seen. Mj cannot be very high on account of its proximity 



