266 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Mar. 11, 



which is raised, but not sufficiently to attain the importance of a cusp, 

 although homologous to the rear cusp of the anterior tooth. The 

 centre of the crown is occupied by a hollow — smooth, and, as it were, 

 scooped out, and depressed considerably below the raised margins. 

 A well-marked chasm intervenes between the marginal edges, both in 

 front and behind, the latter being narrower and less pronounced, so 

 than when the tooth is viewed endwise, the opposite rows are seen 

 apart somewhat as in the tooth of Microlestes. The crenation of the 

 outer margin into a row of tubercles is more decided in Microlestes* 

 (fig. 16), the crown is narrower and more elongated in proportion, 

 and the opposed rows are more approximated. None of the raised 

 points of these teeth in Plagiaulax minor show any considerable 

 marks of abrasion, nor exposure of the ivory : the white spots in 

 the figures represent adherent specks of matrix, and not depressed 

 discs of wear ; the apices of the outer crenations alone are a little 

 worn in the last molar. The animal from which the fossil was derived 

 is inferred, from the intact condition of the molar teeth, to have been 

 a young adult, as these teeth have been found well worn in one 

 specimen of the other species. 



In the jaw of Plagiaulax Becklesii (figs. 1 & 4), there are three 

 small pits on the alveolar border of the hind fragment (c, d), be- 

 hind the last premolar. The anterior two, seen upon the fragment 

 fig. 1, «, 5, are closely approximated, with a thin plate intervening, 

 indicating that they are the sockets of the two-fanged first molar. 

 One of them is shown in the niche at the apex of the vertical sections, 

 figs. 2 & 3, /, g. The last pit, fig. 4, ^, is larger, square, and undi- 

 vided, but showing obsolete marks of a mesial constriction, and indi- 

 cating that the second or last molar had fangs converging in a common 

 socket. The rim of this socket is distinctly defined, and the inner 

 wall raised into a prominent gibbosity which leaves a deep impression 

 on the matrix. This gibbous point corresponds with what occurs 

 in the lower jaw of the recent Hypsiprymnus Gaimardi^ with which 

 it was compared, and is commonly seen on the alveolar wall of the 

 last molar of other animals. 



In the second specimen o^ Flag. Becklesii, figs. 7-10, already re- 

 ferred to, the two true molars of an adult and, judging by their wear, 

 well-aged animal, are seen in situ. They present the same general 

 characters as the corresponding teeth of Flag, minor (fig. 15), but 

 appear to be proportionally larger, in comparison with the premolars. 

 The crown of the first molar bore, as in the other species, three prin- 

 cipal points, two to the inner row ; and to the outer a single tubercle, 

 which is situated more anteriorly than in Flag, minor. The outer 

 point is worn down and indistinctly defined, the wear involving what 

 appears to have been the bevelled lunate rim at the posterior end, as 

 described in the other species. It is not determinable whether it 



* I am indebted to Sir Charles Lyell for the only available means of instituting 

 a comparison of these mammalian teeth from Purbeck with those of the Micro- 

 lestes of Pheninger. Besides several duplicate casts, he had very careful and 

 highly finished drawings made of the teeth during his last visit to Stuttgart, the 

 whole of which have been placed at ray disposal. 



