14 
the stage of development found m the corythosaurs and the nasals do not 
appear to have 'been hollow. 
The narial passage is partly covered by the upturned lower or external 
edge of the premaxilla back to where the bone divides into upper and lower 
limbs. From here it takes a sharp turn forward and enters the cavity 
within the upper limb, much as in C. excavatus. It has not been possible 
to trace the posterior part of the passage in detail, but it appears to have 
been bounded by the nasals postero-laterally, from where it was deflected 
downward and forward to the internal naris much as in C. excavatus , but 
the nasals do not seem to have extended forward and downward to surround 
the passage. 
The premaxilla is square in front as in T. erectofrons, but its anterior 
portion is longer than in that species. The upper limb is broadly rounded 
to enclose the narial passage as in C. excavatus, and there is a thin inner 
wall where it unites with its fellow, thus separating the right and left narial 
passages. From about mid-length of the crest the upper limb narrows and 
extends backward, as a pointed finger of bone, overlapping the nasal, to 
the extremity of that bone. These tips do not divide the nasals posteriorly 
as they do in Lambeosaurus. The lower limb is very similar to that m 
C. excavatus. Its lower edge is grooved for strong sutural contact with the 
lachrymal and prefrontal. The groove that runs diagonally across the bone 
externally is moderately well developed. This groove is not shown in 
either of the other species. If this groove carried a special blood supply 
into the hood one would not expect it to be well pronounced in forms in 
which the hood was not well developed. 
The nasal rests on the frontal with a strong sutural contact and its 
base extends slightly forward to unite with the prefrontal. The upper part 
of the bone unites with its fellow and extends forward as a broad, thin 
bone roofing the posterior portion of the narial passage or air cavity within 
the hood. From near the centre of the hood it narrows and continues for- 
ward as a broad tongue of bone flanking the premaxilla and covering the 
side of the air chamber. On the side of the hood, between this tongue of 
bone and the lower limb of the premaxilla, there is a considerable space 
that is not covered by bone. Similar uncovered spaces are seen in other 
hooded hadrosaurs where the nasals have not reached their full develop- 
ment. 
Compared with Cory thesaurus or Lambeosaurus the brain-case is not 
so strongly deflected and the frontal is very long. The frontal is some- 
what comparable with that of Bactrosaurus johnsoni Gilmore (20, Figure 
21), but unlike that species it is excluded from the orbital rim by the broad 
union of the prefrontal and postorbital. The anterior edge is thickened and 
upturned to meet the overlying nasal and elevated posterior edge of the 
prefrontal. The anterior edge is slightly overhung by the posterior tip of 
the nasal. The united frontals do not form a pronounced dome as in the 
two other species of the genus. 
The prefrontal seems to be much higher posteriorly than in either of 
Parks’ specimens. It more nearly resembles the prefrontal of Lambe- 
osaurus lambei Parks in this backward elevation, but in its forward 
