1881.] 491 [Cope. 
Measurements. M. 
A anteroposterior ......... .0060 
Demaeeeny ML ; transverse..... seek aaa .0060 
‘ anteroposterior ......... .0055 
Dismeters MIT ; tYaNSVeTSe........2.200- 0043 
Depth of ramus at M.I...... ie tlajaie warewaie sss ateupntns 0115 
Thickness: “€ 8 #© posse ved sendeniedaweaes eas caen .0085 
MI0cLANUS SUBTRIGONUS, sp. nov. Represented 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 WM. 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 I. 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 others. 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 Andsonchus, 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. J, and M. IT; the M. IIT 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 ........... 3 aa alors 0285 
Timotors ok bine Pa. TV § anteroposterior....... -0060 
transverse ..........-. -0050 
: anteroposterior....... .0060 
Digmetets et hase-oF M1, } transverse............ .0060 
; ey anteroposterior....... .0060 
Diameters base of M. IT ; tTANSVETSE... 2... ee eee 0075 
: anteroposterior....... .0040 
Diameters base of M. IIT ; transverse..........-.. -0060 
Mioch“@nus aneustus Cope, American Naturalist, 1881, October (Sep- 
tember 22d), p. 831. The least species of the genus, with the teeth about 
the size of Hyopsodus paulus 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 narrow 
grinding surface, which looks like a combination with an anterior median. 
The latter is, however, not separate on the least worn molars. The 
