MOSASAURUS. 49 
municating through a canal with a funnel-shaped pit at the end of the fang. See 
Plates IX, X, XI. 
The conical crowns of the teeth are curved backward with an inclination inward; 
the curvature being more rapid approaching the apex. ‘They are generally divided 
in front and behind by an acute ridge into an inner and an outer surface. In some 
teeth, apparently belonging to the most posterior of the dental series of the jaws, 
and to those of the pterygoid bones, there is only one ridge, which is situated along 
the back or concave border of the crown. The ridges exhibit a minutely crimped 
and sub-denticulated arrangement,’ which was obliterated by wearing. 
The proportionate extent of the inner and outer surfaces of the crown, as defined 
by the two ridges above indicated, varies very much in the different specimens of 
fossil teeth, apparently according to the position the latter occupied in the dental 
series. 
In those teeth, which I suspect to belong to the anterior part of the dental series, 
the crown has the form corresponding with the descriptions which have usually been 
given as characteristic in general of the teeth of Mosasaurus (Plate IX, Figs. 1, 
2,3; Plate X, Figs. 1, 2,3). It is very unequally divided by the acute ridges; the 
inner surface occupying two-thirds or more of the extent of the crown. The con- 
vexity or transverse curvature of the outer surface forms a short segment of a com- 
paratively large circle; that of the inner surface forms one-half to two-thirds or 
more of a circle, whose diameter is that of the crown. The transverse section of 
the crown might be appropriately called shield-shaped, as represented in the wood- 
cut outlines, Nos. 1, 2, 3. 
In those teeth which are supposed to belong to the middle of the dental series 
the disproportion between the outer and inner surfaces of the crown is comparatively 
trifling, and the transverse section is circular or nearly so (Plate IX, Figs. 5, 6; 
Plate X, Figs. 7-9). 
Teeth attributed to the more posterior part of the dental series have their crowns 
compressed from within outwardly and nearly equally divided by the acute ridges, 
and in transverse section are elliptical with acute poles (Plate X, Fig. 10). 
Finally, the last teeth of the series have compressed crowns, with a single ridge, 
and an ovate transverse section (Plate X, Fig. 4). 
The inner and outer surfaces of the crowns in most of the fossil teeth are une- 
qually subdivided into narrow planes, variable in number. They slightly multiply 
towards the base of the crown, and become fewer and less distinct, or altogether 
disappear towards the apex. They vary in degree of distinctness in different teeth, 
and in many do not exist at all (Plates IX, X, XI). 
he indicates as a maxillary and a palatal tooth of Mosasaurus Hoffmanni. The tooth represented in 
his figure 4 looks as if it may have belonged to near the middle of the dental series. The inner side 
of its fang exhibits a small lenticular excavation; part of the receptacle of a successional tooth. 
Fig. 5, represented as a palatal or pterygoid tooth, I suspect rather to belong to the back part of 
the maxillary series. The two figures are reproduced by Gibbes in Plate I, of his Memoir on the 
Mosasaurus. 
* This arrangement appears not to have been noticed by Cuvier in the teeth of the Maestricht 
Monitor. Ossemens Fossiles, I’. X, 145. 
7 ~~=«~April, 1865. 
