HADROSAURUS. 87 
alluded to, so like one another, and referred to Hadrosaurus, Trachodon, and Igqua- 
nodon, represent three species of a genus allied to, but quite distinct from the true 
Iqguanodon of which the I, Mantelli is the type. 
Figs. 5-9, Plate XIII, represent two specimens of inferior teeth of Hadrosaurus, 
the forms of which agree with that already described. In one (Figs. 5, 6, 7) the 
crown is half worn away, exhibiting the triturating suyface as a shield-like, 
inclined plane, very slightly depressed, bordered by enamel at the inner bow-like 
border, and feebly roughened by a linear crucial ridge, the limbs of which give off 
diverging branches. In the other specimen (Figs. 8, 9) the apex is worn off so as 
to present a small shield-like triturating surface, which is smooth or devoid of a 
crucial ridge traversing it. 
Of the two teeth of Hadrosaurus, supposed to have belonged to the upper jaw, 
one is an unworn crown, and is represented in Figs. 10-13, Plate XIII; while the 
other is the crown of a smaller tooth, with its apex worn off, and retaining part 
of the fang, and is represented in Figs. 14-17. 
The superior unworn crown, in comparison with that of the inferior tooth, pre- 
sents a rather demi-ovoidal than a demi-conoidal form, but differs further from the 
comparatively enormous degree of projection of its carina. 
The lozenge-shaped enamel surface, Fig. 10, which is to be viewed as the external 
one, or the reverse in position of that of the inferior teeth, is wider at the two extre- 
mities and slightly narrower at the middle than in the latter. It extends outwardly 
upon a carina, which starts from the apex of the crown, and gradually increases in 
depth until it nearly equals half the diameter of the tooth from without inwardly. 
The apex of the crown is much more blunt than in the lower tooth, and the bottom 
of the enamel surface forms two sides of a triangle, the apex of which is the bottom 
of the edge of the carina. The lateral angles are also more obtuse than in the 
lower teeth. The groups of tubercles ornamenting the lower borders of the crown, 
especially approaching the apex, are also somewhat larger. 
The inner portion of the crown (Figs. 11, 15) is subdivided into four planes, of 
which the intermediate pair extend from the apex to the base, while those on each 
side extend from the apex to near the position of the lateral angles of the crown. 
‘The basal half of the crown on each side presents a somewhat depressed ellip- 
soidal surface, with a narrow prolongation extending upon the fang (Figs. 12, 13, 16, 
17, a), corresponding with the triangular bevelled planes of the inferior teeth, and 
like them exhibiting marks as if they had been adapted to fit or come into contact. 
with lateral successional teeth. Unlike, however, those of the inferior teeth, these 
surfaces of the superior teeth exhibit on both sides the series of impressions 
induced by the tuberculated borders of the crowns of the successional teeth. 
Between these lateral surfaces of contact with the latter, the base of the crown is 
excavated, forming a narrow depressed tract (Figs. 11, 15, 17, 6), continuous with a 
wide shallow groove of the fang, adapted to fit the apex and outer part of the 
summit of the crown of a successional tooth from above. 
The fang of the superior teeth appears from the specimens to have been propor- 
tionately narrower than in the inferior teeth, and further appears mainly to spring 
from the enamelled portion of the crown instead of the opposed portion as in the 
