10 
The prevomers are represented by two very thin bones, which were 
found with the disarticulated skull (Figure 2, Pv.}. They are unlike any 
other prevomers known to the writer, but the internal narial vacuity is 
also very different from that usually seen in reptiles. When viewed from 
the side the prevomer is triangular, with the supero-posterior angle about 
90 degrees and the anterior point extending well forward. This point 
becomes much broader than the main part of the bone, is flat below, and 
rises gently in a low median ridge superiorly. The bone stood upright 
in the posterior nares and the forward prolongation apparently united 
with the premaxilla and maxilla, but this forward articulation cannot be 
determined with certainty. Posteriorly the sides of the bone flare out into 
vertically placed flanges which extend down the posterior edge for more than 
half its length. A moderately sharp ridge runs down the posterior edge and, 
with the flanging sides, makes a double articulating surface for union 
with the thin, upturned edges of the palatine and pterygoid, the central 
ridge fitting between the two bones and the thin out-turned edges covering 
them. Below mid-height the flanges and ridge disappear and the bone con- 
tinues downward to a blunt point. This postero-inferior tip of the right 
prevomer is shorter than that of the left. Except for the expanded 
anterior tip and the flanged posterior edge, the bone is very thin throughout. 
When the bones are properly placed in the skull, they form a high, 
thin division of the posterior nares. There is no indication of sutural con- 
tact between the prevomers on the mid-line, but it would appear that 
they were not widely separated. They measure 145 mm. in length (superior 
surface), 110 mm. in height (posterior edge), and are less than 2 mm. 
thick. 
MANDIBLE 
The dentaries and predentary were preserved naturally articulated 
(Plate II, figure 1) , thus giving the shape of the lower beak and the posterior 
breadth of the mandible. With the predentary is preserved the impres- 
sion of the left half of the horny beak. It extends 36 mm. beyond the 
predentary bone both on the side and in front and shows that the horny 
sheath was quite thick and formed a broad, squarish, duck-like bill. 
The predentary is broad, flat, and fairly straight in front. It is rela- 
tively broader than in C. intermedins, but the main portion of the bone has 
a greater fore and aft diameter. The three sharp keels on the superior 
face are similar. When viewed from below (Plate II, figure 2) the pre- 
dentary is seen to be less horseshoe shaped than either C. intermedins (14, 
Plate V) or Lambeosaurus lambei (5, Figure 11). This is the result of 
greater breadth of the bases of the postero-lateral processes. The thin 
bifurcated flange, which extends backward and slightly downward to 
embrace the lower antero-internal tips of the dentaries, is set farther back 
than in C. intermedins and the wings are relatively much shorter and 
broader. On either side of the base of this flange is a large foramen, 
which pierces the bone, and external to each tip is a smaller, but well- 
defined, foramen entering the dentary. 
The dentary is moderately massive and the coronoid process is short 
and set well out from the main body of the bone. It is only slightly 
decurved anteriorly and the edentulous portion is relatively short and low. 
