44 
is thinly compressed transversely, with an upwardly turned hook at the 
extreme posterior end. Antero-posteriorly the surangular has a greatest 
length over all of about 185 mm. 
The dentary is comparatively narrow vertically, with a short eden- 
tulous border that is abruptly decurved in front. It is deeply excavated 
posteriorly by the mandibular fossa. This fossa is confluent in front with 
the rapidly diminishing Meckelian groove, which extends forward intero- 
inferiorly on the inner face of the dentary to about the middle of its length, 
whence it passes more to the ventral surface of the bone, but continues 
nearly or quite to the symphysis as a very shallow, ill-defined channel. 
The symphysial border is relatively short, measuring 70 mm. in a fore- 
and-aft direction. The coronoid is of moderate size and comparatively 
short. The dentary at this point has a greatest height over all of 184 mm. 
On the posterior end of the dentary, extending backward from the base of 
the dental magazine, is a transversely flattened but pointed process that 
laps a thin vertical process from the superior surface of the surangular. 
Internally this dentary process is closely overlapped by the prearticular. 
The broad, thin ventral termination of the dentary strongly underlaps the 
surangular in the usual manner. In the type dentary there are 41 vertical 
series of teeth, whereas in specimen No. 351, Geol. Surv., Can., only 40 
rows can be detected. These occupy a longitudinal space 315 mm. in 
length. At the base of each row is the usual foramen, these being arranged 
in a curved row following the contour of the lower border of the magazine. 
The predentary is present in all three skulls now before me, but in 
none is this bone perfectly preserved. Its form and principal characters 
are well shown in Figure 11. The predentary in Lambeosaurus is a broad 
U-shaped bone, truncated in front, with two pointed posteriorly directed 
processes that loosely articulate on the inferior side with the decurved 
edentulous portions of the dentaries. Viewed from above, a thin but 
high longitudinal ridge is developed on the inner superior surface of these 
processes, forming a sharp cutting edge. The horny coverings which in 
life enveloped the expanded premaxillaries and predentary were probably 
nicely adjusted to one another, forming an efficient cropping organ for 
procuring food. Superiorly the broad beak portion of the predentary is 
shallowly concave from side to side, with the front edge curving slightly 
upward and to an obtuse edge. This edge, in the type, is formed of 
scalloped bony tooth-like projections, which at their bases have the bone 
perforated by foramen-like holes arranged in a transverse row. 
The predentary is wider than the expanded premaxillaries, but does 
not extend as far forward as those elements. On the median postero- 
inferior surface there is a broad bifurcated process which receives the 
symphysial ends of the dentaries. Each dentary is underlapped by a 
posteriorly directed branch of this process, as shown in Figure 11 A. Above, 
at the centre of the predentary, is a sharp longitudinal ridge that is extended 
backward as a pointed projecting process, which overlaps the median 
symphysial junction of the two dentaries. There is no bony separation of 
the predentary interposed between these symphysial borders of the dentary 
and they have a direct ligamentous union. 
