7 
Horizon: About 200 feet above level of the river, Belly River formation, 
Upper Cretaceous, 
The specimen here provisionally associated with the manus of Chiros- 
tenotes pergracilis consists of the greater part of the left dentary and 
the median part of the right of one individual. The association of these 
specimens is purely arbitrary, as No. 343 was discovered three years after 
the type and a few miles distant from the type locality. The extremely 
long and slender dentary suggests Ornithomimid affinities when contrasted 
with the toothless jaw of Struthiomimus , but the known Coelurid jaws are 
also narrow and slender, though relatively short, and even though the 
present association should prove incorrect it is at least of great interest in 
showing the presence in the Belly River fauna of another moderate-sized 
carnivore that is clearly distinct from either Struthiomimus or Dromm- 
osaurus. 
The left dentary, although having parts missing from both ends, has 
a greatest length of 193 mm., showing that in this dimension it considerably 
exceeds the known Struthiomimus dentary, but in height forward of the 
midlength they are co-equal. Viewed from the side the lower border is 
sinuous, with a strong upward curve at the anterior extremity. The 
external surface of the dentary near the anterior end is everywhere perforated 
by numerous foramina, which continue posteriorly in two nearly parallel 
rows. The upper row evidently ends with the posterior tooth, whereas 
the lower is continued farther back as a long, shallow groove, as shown in 
Figure 3 A. On the internal side the dentary is traversed by the horizontal 
Meckelian groove, which rapidly fades out posterior to the last tooth. 
In the left dentary alveoli for thirteen teeth can be clearly distinguished, 
and comparison with the better-preserved portion of the right dentary 
shows that there were at least three more at the posterior end of the series. 
Allowing two as the number present in the missing anterior end, there were 
at least eighteen teeth in the complete series, a greater number than known 
in any other carnivorous dinosaur from North America above the Triassic, 
as is shown in the following table. 
Dentary Teeth of Theropodous Dinosaurs 
Chirostenoles pergracilis 
Ceratosaurus nasicomis Marsh 
Antrodemus valens Leidy 
Gorgosaurus libratus Lambe 
Tyrannosaurus rex Osborn. 
Ornitholestes hermanni Osborn 
Dromososaurus albertensis Matthew and Brown 
18+Belly River formation 
15 Morrison 
15 
14 Belly River 
13 to 14 Lance 
12 Morrison 
10 Belly River 
In the median part of the dental series ten teeth occupy a longitudinal 
space of 76 mm. Between the alveoli are thin alveolar septa. That 
interdental “rugosse” were developed is indicated by the presence of a 
complete one between the third and fourth tooth of the left dentary, but 
all others are missing. The longitudinal groove for the dental artery is 
plainly shown in the right dentary. 
The forward extent of the missing splenial may be tentatively deter- 
mined as ending at the centre of the thirteenth alveolus, as indicated by 
a narrow longitudinally striated surface on the lower border of Meckel’s 
