84 
BUNOTHERIA. 
are those of the Creodonia. The form of these incisors, with their anterior 
enamel hand and growtii from persistent pnlps, is that of the order Rodentia. 
In all respects, however, there is relation to the Insectivora of the type of the 
ErinacekJm (Hedgehogs). In the latter, the molars and posterior pre¬ 
molars have the same tnbercnlar character, and the inferior molars are 
similarljr composed of two Vs, with the apex outward, an arrangement 
which is indeed common to a majority of the Insectivora. The reduced 
canines and exterior incisors of TillotJierium are again repeated in Erinaceus^ 
and the enlarged incisors separated by an interval, are common to both 
types. The essential difference in the structure of the incisors entitles the 
TiUodonta to a position as a distinct suborder of the Insectivora, but the 
interval is diminished by the genus EstJionyx. This genus, wdth the molar 
teeth of the type common to the two groups, presents incisors which are 
intermediate in character. While the anterior face only is covered with 
enamel, and tlie edge is thus scalpriform, the latter is not persistently 
developed, but terminates at a point which obviously distinguishes crown 
from root. The combination of “characters of Carnivores and Ungulates” 
^‘with those of Rodents, supposed to exist by Professor Marsh, is thus not 
obvious. 
IV. 
Another group of this order was discovered by the writer in New 
Mexico, and is an especial subject of this report. They differ from the pre¬ 
ceding, and all other Mammalian types, in the structure of their superior 
incisor teeth. These have two band-like enamel faces, one anterior and the 
other posterior, the result of which is a truncate or concave extremity of the 
crown on attrition. The inferior incisors are Rodent-like, with an anterior 
enamel band only. This group I have called the Tceniodonta. So far as 
known, tlie structure of the molar teeth is more simple than in the TiUodonta^ 
and the enamel is reduced in its extent, being chiefly present in bands on 
their external faces. In one genus, Calamodon, the surfaces thus left 
uncovered are invested with a layer of cementum. 
V. 
It appears to me that the four divisions above defined are not separable 
as orders from each other, but are connected by very close gradations. It 
