10 THE ROYAL SOCIETY OF CANADA 
T. marginatus and T. altidens, distinguished, among other characters, 
by differences in the mode of succession, form, and marginal ornamenta- 
tion of the teeth. These dinosaurs were bipedal, herbivorous, and with- 
out heavy armour as is shown by specimens from Wyoming in which 
the impression of the skin is preserved. Osborn in describing one of 
these wonderful “mummified” Trachodons states that the skin was 
apparently very thin and that its surface was devoid of either coarse 
tubercles or of overlapping scales, but covered with larger pavement or 
non-imbricating scales and smaller tubercular scales. The same 
authority further mentions that the “manus is completely encased in 
the integument, and was thus web-footed.” 
No remains of Sauropoda have been found in the Judith River beds. 
The subject of the world-wide distribution of the Dinosauria 
throughout nearly the whole of the Mesozoic period has been treated in 
a most able manner lately by Lull who calls attention to “their great 
numbers both of individuals and kinds, and the amazing range of their 
adaptations.” That their range northward in this country was great 
has been proved by the finding of a vertebra of a carnivorous dinosaur 
in rocks of Mesozoic age in Bathurst island far north of the Arctic circle. 
A lately described Crocodilian genus Leidyosuchus, a proccelian, 
brevirostrate form of Eusuchia occurs at this horizon and curiously 
combines characters which have been ascribed to the genera Crocodilus 
and Alligator. The genus, however, approaches closer to the croco- 
diles than to the alligators. 
An extremely interesting feature of the Judith River fauna is the 
presence of primitive mammals, whose appearance at this time is the 
first indication we have of mammalian life in this country, and whose 
remains are the only known ones from our Cretaceous rocks. Two 
species are represented, Ptilodus primevus and Boreodon matutinus. 
The former is an Archaic Marsupial, a Multituberculate of the family 
Plagiaulacidæ and is the earliest known species of the genus. It was 
founded on aright mandibular ramus having the fourth premolar and 
the first molar in place. The latter was established on a double-rooted 
premolar with which has been provisionally associated an imperfect 
lower jaw, without teeth, found by Hatcher in beds of Judith River age 
on Milk river. The position of the genus is problematical but appar- 
ently the animal has marsupial affinities. 
We can picture to ourselves the low lying country of Judith River 
times, the swamps, lakes and lagoons, the land but little elevated above 
the water with, probably, in the dim western distance the outline of 
the nascent Rockies. In the waters are crocodiles, and turtles of 
various kinds, more in evidence than the fishes and the numerous 
molluses of entr types., In the swamps and on the margins of 
