222 ROYAL SOCIETY OF CANADA 
The question arises—may not this species from Alberta be a direct 
descendant of one of the brevirostrate forms of the amphiccelian Gonio- 
pholidæ, (Purbeckian and Wealden), having adopted a proccelian type 
of vertebra but still retaining the splenial in the symphysis. In the 
genus Goniopholis for instance the splenial enters the symphysis to a 
slight extent, also the teeth are longitudinally grooved, a resemblance 
indicated by the very faint fluting of the teeth of Leidyosuchus. In 
this connection it is interesting to note that the Judith River (Belly 
River) fauna harks back in a number of instances to Jurassic forms. It 
includes turtles of the Jurassic family Pleurosternide, Plesiosaurs and 
specialized Stegosaurs; a species of Ornithomimus (OQ. altus) is pro- 
bably a successor to the Upper Jurassic Ornitholestes. 
-MANDIBLE OF LEIDYOSUCHUS. 
The parts of the lower jaw, found together, consist of two pieces 
from the front and back halves of the left ramus almost completing 
its length (plate I, figs. 1, la, 1b). A portion at mid-length (restored 
in the figure) consisting principally of the posterior ends of the dentary 
and splenial bones, was not recovered. The specimen lacks the 
articular and coronoid elements, and the anterior end of the dentary, in 
advance of the alveolus for the third tooth, is missing. The alveoli of 
the third and succeeding fifteen teeth are preserved and it is possible 
that another tooth or perhaps two may have occurred posterior to the 
eighteenth behind which the fracture in the specimen occurs. Judging 
from the alveoli the fourth tooth was the largest, the third was nearly 
if not quite the size of the fourth, the fifth to the tenth were small and 
of nearly equal size, the eleventh, twelfth and thirteenth were slightly 
and about equally enlarged, posterior to the thirteenth the teeth 
gradually decreased in size to the eighteenth which was of about the 
size of those immediately behind the fourth. The bases of the fourth, 
fifth and sixth teeth are preserved in their sockets. The alveoli are 
complete apparently to and including the ninth, beyond this the bony 
divisions separating them are gradually less developed and take the 
form of ridges, on the inner side of the outer wall of the dentary. These 
ridges decrease in prominence backward until, between the last three 
teeth, there is only a slight indication of separate sockets, an evidence 
probably of immaturity in the individual. 
Viewing the mandible from the side the outline of the dentary 
below, in advance of the anterior end of the angular, is straight and 
horizontal to the slight upturn of the extremity beneath the .alveolus 
for the first tooth, the exact form anteriorly being given by the specimen 
