total length is four inches ; its outer face is convex in every direction, but more strongly so from above downwards near the anterior end, and is marked by a longitudinal groove running parallel to, and at a distance of about a fourth of an inch from the upwardly curved dentigerous border : this groove (Pl. XIX. fig. l, g), doubtless, gave lodgement to a vessel and a branch of the fifth pair of nerves from which neuro-vascular filaments were sent off for the supply of the teeth through the foramina that pierce the bottom of the groove. Numerous vascular foramina stud the surface of the bone near the end, which is flattened into a facet (figs. 1, 2, f) looking upwards and forwards : above, it presents for its posterior half a thin irregular fractured edge ; its greatest depth is measured from the angle formed by the junction of this fractured edge with a natural free edge which, sloping downwards and forwards, and curving very little outwards, forms the left lateral boundary of the external nasal aperture.
The removal of a small portion of the matrix revealed the existence of a small bony projection (figs. 1, 2, 6) from the inner face ; this met with a similar projection from the opposite praemaxilla, and furnishes evidence that the points at any rate of the non-confluent praemaxillae entered into the nasal aperture ; but whether they were so extended upwards and backwards in the middle line as to meet in lacertine fashion the forward prolongation of the nasals, the limited extent of my materials will not allow me to determine.
The dentigerous edge ( = outer alveolar wall) supports eight teeth, the posterior of which only exhibit perfect bony union of their bases with the alveolar margin ; the rest are less firmly united to their shallow sockets. This creature evidently had two teeth in front on each side of the middle line ; the remains of the inner of these were disclosed by the development of the fossil, but the shallow socket of the other is the sole evidence of its existence ; immediately behind, and touching the third tooth, is what appears to be the osseous base (fig. 1, c) of a shed tooth.
The projection from the inner face at (a) in fig. 3, which represents the fractured hind end in section, appears to be the rudiment of what would have been produced inwards and downwards, so as to form the inner alveolar plate, if the teeth had been lodged in a continuous groove or in distinct sockets, and not anchylosed to the terminal border of the external alveolar plate. The teeth are precisely similar in shape to those in the anterior region of the mouth in Monitor niloticus ; but I do not wish to be understood as suggesting that the posterior teeth were similarly modified for crushing : the smoothness of the enamel is only broken by the faintest trace of folding at the point of its junction with the cement ; this is finely furrowed or striated longitudinally, as in the teeth of Mosasaurus and M. niloticus. The bony bases, which bear nearly the same great proportionate size to the crown as in Mosasaurus, were no doubt covered by a gum. The pulp-cavities remain open.
This reptile differs from Mosasaurus in the apparently persistent distinctness of the praemaxillae from each other, and their small development in the middle line, in the more anterior position of the
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