63 
Geographic and Geologic Occurrence 
The genus Hypacrosaurus has only been recognized from a compara- 
tively restricted area along Red Deer river, Alberta, with a single occurence 1 
in the Two Medicine formation in northern Montana. The latter occur- 
rence perhaps needs additional verification. However, in the light of this 
newly discovered skeleton, with which the remains of the Montana speci- 
men closely agree in measurements, it appears to give credence to the 
correctness of the original identification. 
It will be noted in the table of comparative measurements that the 
few bones available for comparison are remarkably close in their propor- 
tions. Attention is also called to the short, strongly-decurved, edentulous 
portion of the dentary, of the Montana specimen, which, with the reduced 
number (40) of vertical tooth rows points, quite conclusively to its being 
one of the Lambeosaurinse, a group to which we now know Hypacrosaurus 
belongs. 
With the above-mentioned exception all the other known specimens, six 
in number, have been found within 5 miles above and 16 miles below Tolman 
ferry. Although no special significance may be attached to the fact, yet 
it is of interest to know that of the four specimens collected by Brown 
and identified by him as belonging to Hypacrosaurus altispinus , none of 
them was found in geological levels exceeding 70 feet above the river, 
whereas the present specimens come from levels 175 feet and 115 feet 
respectively above the stream. 
Whether it will ever be possible to identify horizons within the Edmon- 
ton and Belly River formations by their contained dinosaurian species is 
exceedingly doubtful, but the possibility of their contributing to a better 
understanding not only of geologic but also of palaeontologic problems is 
sufficient reason why careful records should always be kept of the levels 
from which specimens are obtained. 
Relationships 
The discovery of the present specimen, having a nearly complete skull, 
with high, helmet-like crest; fronto-parietal region reduced; nasals receding; 
anterior nares separated by premaxillaries, which are greatly prolonged 
backward and enter largely into formation of the crest; reduced lachrymal; 
reduced number of vertical tooth rows; and an ischium greatly expanded 
distally; at once shows that the genus Hypacrosaurus is a true member of 
the sub-family Lambeosaurinse as originally characterized by Lambe 2 . 
Long before the skull of Hypacrosaurus was known Brown 3 called attention 
to the similarity in structure of the genera Hypacrosaurus and Corytho- 
saurus and suggested that “the two genera are closely related, and Corytho- 
saurus may have been the ancestor of Hypacrosaurus” . The skull structure, 
as now known, affords additional evidence of the close affinities existing 
between these two genera and I see nothing in the skeletal structure of the 
latter that could not very well have been evolved from the earlier Belly 
River Corythosaurus. 
1 Prof. Paper 103, U. S. Geol. Surv., 1917, pp. 38-41, text Figs. 48-53. 
2 Geol. Surv., Can., Mem. 120, 1920, p. 68. 
* Bull. Am. Mus. Nat. Hist., vol. 35, 1916, p. 710. 
