1869.] MASON ACEODOIirTOSATJEFS. 443 



total length is four inches ; its outer face is convex in every direc- 

 tion, 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 den- 

 tigerous border : this groove (PL XIX. fig. l,g), doubtless, gave lodge- 

 ment 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 

 thi^ough 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 fractui^ed 

 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 exist- 

 ence of a small bony projection (figs. 1, 2, 6) from the inner face ; this 

 met with a similar projection from the opposite praemaxilla, and fur- 

 nishes evidence that the points at any rate of the ^ion-confluent prae- 

 maxillae 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 sodkets. 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 repre- 

 sents 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 pre- 

 cisely 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 prsemaxillse from each other, and their small de- 

 velopment in the middle line, in the more anterior position of the 



VOL. XXV. PAET I. 2 H 



