HADROSAURUS. 85 



in the same manner as in living Lacertians. In Eadrosaurus 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 XIII. 



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 croAvn, 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 lovrer 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 seeii in Figs. 3, 4, c. 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, c. 



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 successionai 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 Avas 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 cro^vn, of 

 which it is an extension without the enamel. Its outer border continues the slope 



