36 
“In Stephanosaurus [Lambeosaurus] the top of the skull bears a high 
hood or crest, narrow from front to back, and laterally compressed, from 
whose posterior base there is a comparatively slender backward prolonga- 
tion forming a process which reaches far beyond the occiput at a consider- 
able distance above the level of the parieto-squamosal bar. The crest 
with its posterior extension is made up of the premaxillary and nasal bones. 
The inferior portion of the premaxillaries is greatly expanded posteriorly 
to form the central, lower part of the crest proper on either side. [In this 
respect it approaches the crest of Hypacrosaurus ]. Superiorly the premax- 
illaries form the whole of the crest above, rising vertically in front and 
descending as steeply behind, thence continuing backward to take part 
in the formation of the posterior process. The nasals extend obliquely 
upward and forward from in advance of the small frontals and appear 
externally in the crest between the broad hinder termination of the inferior 
part of the premaxillaries (which cannot properly be referred to as a lower 
limb of the premaxillary) and the posterior descending portion of the 
premaxillaries above. They also extend narrowly backward beyond the 
frontals as part of the crest prolongation constituting the lower surface 
of the process, embracing the premaxillaries from below, and more posterior- 
ly enveloping them externally also. In the back part of the crest, therefore, 
and in the crest-prolongation, the premaxillaries are between the nasals, 
that is along the whole of the latter’s length. A long, narrow vacuity in the 
crest occurs between the nasals and the lower premaxillary expansion.” 
This vacuity is even more pronounced in specimen No. 351, Geol. 
Surv., Can. (Plate VII). A somewhat similar opening is found in the 
skull of Corythosaurus excavatus Gilmore, in the University of Alberta 
collections (Can. Field Naturalist, vol. 37, No. 3, 1923, Fig. 1), but in that 
specimen it is confluent with the more anterior horizontal vacuity, 
developed as in Corythosaurus casuarius Brown. 
“The depth of the skull above its midlength is equal to its total length. 
Viewing the skull from the side, the facial outline is sigmoid, at first concave, 
ascending rapidly from the front until it is vertical, whence it continues 
upward and reaches a point directly above by an even convex curve. 
“A broad, shallow groove runs obliquely upward and slightly back- 
ward across the lower portion of the premaxillary a short distance in advance 
of the anterior end of the jugal. [A similar groove is also present in Cory- 
thosaurus, Hypacrosaurus , and Cheneosaurus .] This groove was considered 
to mark the back termination of the lower part of the premaxillary (“lower 
limb of the premaxilla”) in the original description of the skull of Stepha- 
nosaurus . What was then named prefrontal is now clearly seen to be the 
greatly expanded postero-inferior part of the premaxillary as the structure 
of the bone is continuous across the groove.” 
The frontal, as Lambe has pointed out, is excluded from the orbital 
rim by the prefrontal and postorbital, and this is true of all members of 
the Lambeosaurinae. It lies almost entirely under the anterior, lower 
surface of the posteriorly directed naso-premaxillary process. The frontals 
are very much reduced in size, being wider than long, with a deep vertical 
suture at their anterior ends for union with the nasals and prefrontals, as 
shown in a fragmentary specimen, No. 8502, This vertical sutural surface 
has a greatest depth that is nearly equal to one and one-half times the 
greatest length of the frontal bones. 
