9 
advance of this fenestra the right and left narial passages are completely 
separated by bone. Of course it is possible that these fenestrae were closed, 
in life, but their similar size, shape, and position suggest that they do not 
represent incompletely calcified areas. Aside from these there is no fene- 
stra through the premaxilla or nasal. 
This more detailed study of the narial passages and large air reservoirs 
does not seem to bear out the theory that the elongated air passage was for 
trumpeting and was possessed by the males only. It seems more likely 
that they assisted the animal in feeding under water. The double-trapping of 
the air would prevent water from getting into the lungs when feeding in the 
swamps and the extra supply of air might also permit longer submergence. 
The cranium resembles that of C. intermedins, but the sutural surface 
on the frontal, for articulation with the nasals, is longer and less steeply 
inclined. The occipital region is low and lacks the conspicuous overhang 
seen in Edmontosaurus and other flat-headed hadrosaurs. 
The supraoccipital is well defined and shown, beyond question, to 
be well removed from the foramen magnum. It is roughly triangular with 
the broad base on the coalesced exoccipitals and the rounded apex extend- 
ing under the united posterior borders of the squamosals. Its stage of 
development is intermediate between that shown by Gilmore for Bactro- 
saurus johnsoni (6, Figure 22) and that prevailing in Thespesius saskatche- 
wanensis Sternberg (16). 
approximately X 
The maxilla (Plate I, figure 2, Mx; Figure 2) resembles that of C. 
intermedius, but the vascular groove on the internal surface of the bone, 
above the alveolar border, turns up and is deeper posteriorly and there are 
only 39 vertical rows of teeth as compared with 43 in Parks’ specimens 
and the maxilla of C. intermedius No. 8704, Geol. Surv,, Canada. In more 
than half of the tooth rows there are tw T o functional teeth in the triturating 
surface. The total length of the maxilla is 280 mm. and the alveolar 
length is 240 mm. 
