1892.] NATURAL SCIENCES OF PHILADELPHIA. 803 



archeil from side to side and continued forward into an extremely 

 prominent sagittal crest. The zygomatic arches are heavy and pro- 

 ject strongly from the skull ; the glenoid cavity is deeply concave, 

 with prominent pre- and post-glenoid crests. The mandible varies 

 much in size and proportions among the difterent si)ecies, being in 

 some long and slender and in others very massive, but in all the 

 ascending ramus is of remarkable antero-posterior extent, the dis- 

 tance from the condyle to in^ exceeding the length of the molar pre- 

 molar series. The condyle is ])laced low down and there is a short 

 hooked angular process. The masseteric fossa is large but shallow, 

 especially so in the larger species. 



In his latest paper^ on the Puerco fauna Cope classifies Sareo. 

 thraustes as a subgenus of MiocUmiis, a view which is obviously unten- 

 able, as the affinities of the genus are much more nearly with the 

 Mesomjchidce, in which family Schlosser has included it. 



There are five well marked species o^ Sareothraustes, all of which 

 are from the Puerco beds : S. antiquus Cope, IS. coryphceus Cope, S. 

 bathygnathus Cope and S. ( Conorydes, Miocleenns) crassiciispis Cope. 



MESONYCHIDJE Cope. 



Superior molars tritubercular, not trenchant ; inferior molars with 

 metaconid rudimentary or absent; talon trenchant, lacking ento- 

 conid. Astragalus deeply grooved, except in Dissacus, and articu- 

 lating with the cuboid. 



The long continued existence of this family, throughout the entire 

 Eocene and into the White River Miocene, brought with it numbers 

 of important changes in dental and skeletal structure, so that char- 

 acters diagnostic of the entire family are difficult to find, and yet 

 the close relationship and succession of the various genera are so 

 clear and obvious that it is impracticable to place them in more than 

 one family. 



DISSACTJS2 Cope. 



This, the oldest member of the series, is in many respects closely 

 similar to Goniacodon and Tn'isodon, but with important differences. 

 The dental formula is unreduced, but the upper premolars have 

 already attained a considerable degree of complication. P3 is much 

 elongated antero-posteriorly and has a small deuterocone ; P4 is com- 

 pletely molariform, having a distinct tritocone in addition to the 



1 Trans. Am. Phil. Soc, Vol. xvi, Pt. II. p. 3:^0. 

 2Amer. Naturalist, 1881, p. 1019. 



