1881.1 4:^1 [Cope. 



Measurements. M. 



,_ _ c anteroposterior 0060 



Diameters M. I < , nnon 



i transverse , 0060 



Diameters M. Ill 



( anteroposterior 0055 



\ transverse 0048 



Depth of ramus at M. 1 0115 



Thickness " " " 0085 



MiocL^Nus SUBTRIGONUS, sp. nov. Eeprescntecl by a portion of a cra- 

 nium anterior to the orbits and lacking the extremity of the muzzle, dis- 

 torted by pressure. It exhibits nearly all of the molar teeth. The spe- 

 cies differs from M. turgidus in the greater acuteness of all its cusps, and in 

 the equilateral form of the fourth premolar. It is too large to belong to 

 the M. angustus, which is represented by a mandible only ; and too small 

 to be the M. mandibularis, whose maxillary dentition is unknown. 



The inner borders of the molar teeth are shorter than the outer, espe- 

 cially in the last two molars. The last true molar is smaller than either 

 of the othei's. The cusps are all subconical, but the internal is connected 

 with the intermediate by ridges, which give it a triangular section. The 

 latter form a V, homologous with that in Anisonehus, but not so distinct, 

 and the intermediate tubercles are not lost in its branches as in that 

 genus. The posterior inner lobe of that and other genera, is represented 

 by a thickening of the cingulum. This cingulum extends entirely round 

 the P-m. IV and M. I, and M. II ; the M. Ill is injured. The sides of the 

 base of the P-m. IV are slightly concave. The enamel of all the molars is 

 wrinkled. 



Measurements. M. 



Length of bases of last five molars 0285 



-r^. ^ „ , „^ „^ c anteroposterior 0060 



Diameters of base of P-m. IV ^ , „„^^ 



i transverse 0050 



Diameters of base of M. I 



anteroposterior 0060 



transverse 0060 



T^. , „ ,, ^^ c anteropostenor 0060 



Diameters base of M. II \ ^ „„^^ 



( transverse .007.1 



-p.. ^ , „-^ -__^ c anteroposterior 0040 



Diameters base of M. Ill \ ^ '■ „_„_ 



transverse 0060 



MiocL.EXus AKGUSTUS Copc, American Naturalist, 1881, October (Sep- 

 tember 22d), p. 831. The least species of the genus, with the teeth about 

 the size of Hyopsodus panlus Leidy, but with more robust jaw. The molar 

 teeth diminish in size regularly posteriorly from the P-m. IV. They all 

 have three subequal posterior cusps which are less elevated than the ante- 

 rior ones. The median is enlarged into a heel on the last tooth. The 

 anterior are opposite, and the external is larger than the internal. There 

 is no anterior internal. The external wears into an anteroposterior narroAv 

 grinding surface, which looks like a combination with an anterior median. 

 The latter is, however, not separate on the least worn molars. The 



FROG. AJIER. PHILOS. SOC. XIX. 109. 3j. PRINTED OCT. 21, 1881. 



