356 Wo7'tma7i — Sticdies of Eocene Mainmalia in the 



it posteriorly as well as in front. The canine or second pre- 

 molar follows withont diastema, and judging from the size of 

 its alveolns was relatively large. An indistinct ridge npon the 

 inner side of the socket indicates that the root was grooved in 

 this situation, a fact which is against its interpretation as a 

 canine and in favor of its being a premolar. The third pre- 

 molar had not been fully erupted at tlie time of death, and is 

 only partly protruded from the jaw ; it is implanted by two 

 roots somewhat diagonally to the long axis of the ramus and 

 lias a pointed crown, with a small, though distinct, heel. The 

 fourth premolar is identical in structure with that of the type 

 of M. elegans already described, as are also the molars. The 

 last molar is not preserved in either specimen. The ramus is 

 deepest in front at the posterior border of the symphysis, nar- 

 rowing considerably behind. The tooth line does not pass 

 behind the coronoid to such an extent as in Cheiromys and the 

 Rodentia. The anterior border of the masseteric fossa is prom- 

 inent and, as in both Cheiromys and the Rodentia, toward its 

 upper 2:)Osterior portion forms the root of the coronoid, which 

 therefore has a position much external to the tooth line. The 

 opening of the inferior dental canal lies considerably below 

 the level of the tooth crowns — a character in which it agrees 

 with Cheiromys and differs from both the modern squirrels 

 and Paramys. It may be further noted that the symphysis 

 is roughened, but not coossified with the opposite ramus. 



Description of other Material.- — There are in the Marsh col- 

 lection six other specimens of more or less complete lovv^er jaws, 

 which I refer to this species. Among these specimens there 

 are several examples of a last molar. This tooth very closely 

 resembles the other molars in structure, differing only in the 

 elongation of the heel by reason of the greater size and promi- 

 nence of its posterior cusps. In no case do any of the upper 

 teeth accompany these lower jaws, but in another species to be 

 described later, there are upper and lower teeth in association, 

 so that the form of the upper molars is known with certainty. 

 In my own collection there is a well-preserved upper jaw of a 

 small form of Microsyops, bearing all the molars and the last 

 premolar, which accord so w^ell in size with w^hat the upper 

 teeth of M. elegans should be, that I have no hesitancy in 

 attributing it to that species. I obtained this proportional size 

 by measurement of the teeth of many living species of lemurs, as 

 well as of those of the one known Microsyops above referred to. 



There should be also mentioned here, the species described 

 by Leidy under the name Palceacodon verus, from a superior 

 molar. According to Leidy's figure, this tooth, figure 111, is 

 identical with the upper teeth wdiich I refer to Microsyops 

 elegans^ and it therefore becomes a synonym of that species — 



