HADROSAURUS. 85 
in the same manner as in living Lacertians. In Hadrosaurus the shape of the teeth 
and their markings make it appear as if they were closely crowded, the functional 
and successional series together, so as to produce a vertical quincuncial arrangement, 
as represented in the partially ideal Fig. 19, Plate XITI. 
The specimens of inferior teeth vary slightly in size, and present different condi- 
tions, from one that is unworn, to another which has its crown half worn away. 
An unworn and almost perfect specimen, represented in Figs. 1-4, Plate XIII, 
is twenty-two lines in length. Viewed laterally, Figs. 3, 4, in outline it has the 
form of an obtuse angled triangle, of which the two shorter sides correspond with 
the division of the tooth into crown and fang. 
The crown, separately considered, is trihedral or demiconoidal, and bevelled off 
on each side towards the base internally, and it comprises rather more than half the 
length of the tooth. It widens antero-posteriorly from the summit to the middle, 
and then decreases in the same direction towards the fang. In the reverse direction, 
it increases in breadth from the summit to the bottom of the crown. 
The inner side of the crown, Fig. 1, a, is alone invested with enamel, and forms 
a lozenge-shaped surface divided in its length by a prominent median carina. It is 
slightly convex vertically, and has the borders a little everted, so that the divisions 
of the surface on each side of the carina are slightly concave transversely. The 
upper angle, constituting the apex of the tooth, is rounded, the lateral angles are 
obtuse, and the lower angle is notched. 
The upper borders of the enamelled surface are thickened, rounded, and furnished 
with a series of feeble transverse ridges resolved into minute tubercles, as repre- 
sented in the magnified view of Fig. d. 
The outer surface of the crown, Fig. 2, has a dull aspect; at its upper half is 
paraboloid in transverse section, but below is ellipsoidal. The lower half presents 
at the sides internally a bevelled triangular plane, extending upon the fang and 
marked by vascular grooves, as seen in Figs. 3, 4, ec. One of the bevelled planes, 
Fig. 4, c, next the enamel edge, is marked by a series of impressions, adapted to 
the accommodation of the tubercular enamel border of the contiguous side of the 
crown of a lateral successional tooth. The opposite plane is devoid of this series 
of impressions, as seen in Fig. 3, ¢. 
Evidently it appears from the shape and markings of the bevelled planes just 
described that they were adapted to fit the summits of the crowns of lateral succes- 
sional teeth, according to the plan represented in Fig. 19. 
In the slightly oblique relationship of the functional and successional teeth the 
tuberculated enamel border of one side of. the latter overlapped the contiguous 
lower border of the former in front, while the opposite tuberculated enamel border 
of the successional teeth was overlapped by the contiguous lower border of the 
functional teeth behind. Hence one bevelled surface presents the impression of the 
tuberculated enamel border of a successional tooth, and the opposite surface does 
not. ‘The vascular grooves of the bevelled surfaces are due to the vessels in the 
membrane separating the successional from the functional teeth. 
The fang is laterally compressed, conoidal, and rather shorter than the crown, of 
which it is an extension without the enamel. Its outer border continues the slope 
