41 
Posterior depth of magazine, about 60 
Anterior depth of magazine, about . 84 
Depth of magazine at its midlength, about 145 
Posterior breadth of cutting surface of teeth, about 8 
Anterior breadth of cutting surface of teeth, about 8 
Breadth of cutting surface of teeth at its midlength 30 
Predentary. (Pd.). In the type of Edmontosaurus this bone is in 
place but is mostly concealed beneath the premaxillaries. Its front 
border is injured and throughout it seems to have been distorted and 
crushed. With the further removal of matrix from the specimen, if this 
prove feasible, some general idea of the proportions of the bone may be 
gained from below, but at present its description is not possible. It was 
broad in correspondence with the great exterior expansion of the pre- 
maxillaries, and appears to have been moderately thin in front with a 
development of the notches along the front border so usual in the Hadro- 
sauridse. 
In the paratype of Edmontosaurus the predentary as well as the 
premaxillaries were not found. 
Surangular. (Sa.). Figures 3, 4, 30, and 22. In comparison with 
the angular, articular, and splenial, the surangular is a large, robust bone 
with an extensive attachment to the dentary. It, in conjunction with 
the angular, articular, and splenial, adds considerably to the length of 
the mandibular ramus, and it is principally through this bone that the 
attachment of the mandible to the quadrate is effected. 
The surangular articulates in front with the dentary, postero-superiorly 
with the articular, and laterally on the inner side with the angular. It 
consists of a somewhat oblong main portion, longer than broad, broader 
in front than behind, and thick posteriorly in contrast to the anterior 
half-length which is thinned by having its upper surface excavated. The 
main portion of the bone posteriorly has a backward extension on the 
inner side which thins to the rear, faces upward and inward, and, when 
viewed from above, curves outwardly in outline to a broadly rounded 
termination. The supero-exterior border of this posterior extension is 
continued forward on the upper surface of the main portion as an upwardly 
directed flange which thins to the front where it ends abruptly a short 
distance behind the concavity in the anterior upper surface. This flange 
is close above, and curves in conformity with the inner border of the bone; 
it has a vertical inner face and a sloping outer one. Between the base 
of the flange and the inner border of the bone is a narrow horizontal shelf 
which extends forward with increasing breadth for a short distance beyond 
the flange and is carried back on the inner side of the extension as a groove 
best defined posteriorly. This shelf and groove mark the upper limit 
of the surface of contact between the angular and the splenial. Antero- 
exteriorly there is a prolongation of the main portion of the bone upward 
and slightly forward which ends slenderly above, reaching a height of over 
110 mm., above the general plane of the lower anterior surface. This 
prolongation is laterally compressed throughout, and at its base is directed 
obliquely backward as a ridge toward the vertical flange, bounding the 
anterior concavity externally. 
