74 
2 miles east "of the mouth of Little Sandhill creek. The specimen consists 
of all the cranium and mandible in advance of a line passing irregularly 
down from the front end of the supratemporal fossae, and supplies the shape 
of the mandible, and the true length of the snout which is apparently 
restored to too great a length in the genotype described by Brown in 
1916.^ In the Geological Survey skull the premaxillary and nasal bones 
are complete and give the proper extent and manner of union of the nasal 
anteriorly with the upper limb of the premaxillary, the true outline of the 
posterior termination of the lower limb of the premaxillary, and the position 
and shape of the posterior end of the nasals. Both the upper and lower 
teeth are well preserved. The specimen proves that in Prosaurolophus 
the “crest” is formed entirely from the nasals and not chiefly from the 
frontals as supposed by Brown. In Figure 38F the posterior end of the 
skull is restored from Brown’s figure of the genotype. The skull of 
Prosaurolophus is thus seen to be much shorter than originally described 
and more in accord with the outline of Saurolophus Brown, from the 
Edmonton formation. 
A great advance was made in our knowledge of the structure of the 
skull of Stephanosaurus by the discovery in 1917 in the Belly River forma- 
tion, Red Deer river, of a skull of S. marginatus much more complete 
and better preserved than the one described by the writer in 1914.^ In 
the 1917 specimen (Figure 39H) the extraordinary contour of the head 
is fully given, and as most of the sutures are traceable, the boundaries 
of the various elements are revealed, clearing up points of doubt as regards 
the determination of the bones not only in Stephanosaurus but also in 
Corythosaurus and Cheneosaurus, other known members of the subfamily. 
In the Stephanosaurince the premaxillaries are greatly extended and 
enlarged posteriorly relegating the nasals to a position surprisingly far back 
in the skull. 
In Stephanosaurus 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 prolongation forming a 
process which reaches far beyond the occiput at a considerable 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. Superiorly the 
premaxillaries 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 
owerl 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 pos- 
teriorly enveloping them externally also. In the back part of the crest, 
therefore, and in the crest-prolongation, the premaxillaries are between 
iiull. Am. Mus. Nat. Hist., vol. XXXV, pp. 701-708, figs 1 and 3. 
2The Ottawa Naturalist, vol. XXVIII, pp. 17-20, plate I. 
