414 PLAGIAULAX. 



supports two well-raised and bluntly conical points or tuber- 

 cles, separated by a wide cleft, which is partly continued 

 down upon the body of the tooth, vertically in a sinus, form- 

 ing an obsolete mesial constriction. The points are isolated 

 and start up in considerable relief. The outer edge of the 

 crown is not divided correspondingly ; it supports mesially 

 but a single prominent conical tubercle, which is intruded 

 upon the plateau of the crown, and opposed to the sinus 

 between the two inner points. It alternates therefore with 

 the latter. The base of the outer point is continued on either 

 side, backwards and forwards, in a well-marked lunate be- 

 velled rim, which is convex outwards, and rises at either end 

 into a low terminal lobule. The posterior lobule may be 

 considered as the homologue of the posterior inner point, 

 although it forms but an insignificant tubercle. The an- 

 terior lobule is still less developed, but opposed to the 

 anterior inner point. The middle of the crown is occupied 

 by a sinuous hollow surface, intervening between the outer 

 and inner rows. This hollow, from the intrusion of the 

 outer mesial point and the constriction of the inner side, is 

 divided into an anterior and posterior discoidal depression. 

 The two rows are separated at both ends of the tooth by a 

 longitudinal chasm. There is no indication of any low trans- 

 verse concave ridge connecting the opposed tubercles. From 

 the above description it will be seen that the two sides are 

 unsymmetrical, whether the outer row is considered as con- 

 sisting of a single point with an accessory tubercle on either 

 side, or of three unequal tubercles. 



The second or last true molar (PI. XXXIV. figs. 5 and 6), 

 viewed in profile, is smaller than the first, and the crown- 

 surface, although of nearly equal extent, is less complex in 

 its subdivision. It is of a broad oval, with the base applied 

 to the contiguous anterior tooth. The coronal eminences 

 consist of an outer and inner raised marginal and more or 

 less lobulated edge, separated by a broad central depression. 

 The outer edge is very narrow and nearly horizontal, rounded 

 off at either end and presenting no marks of composition be- 

 yond four or five obscure indications of crenulation, like one 

 of the rows in the tooth of Microlestes (see PI. XXXIV. 

 fig. 7) . It is incurved so as to overarch slightly the central 

 depression. The inner edge presents at its anterior end a 

 well-elevated and isolated conical tubercle, resembling in size 

 and form the outer mesial point of the first true molar. It 

 is bounded posteriorly by a deep wide cleft from which a 

 convex edge is continued backwards, which is raised, but not 

 sufficiently to attain the importance of a cusp, although 

 homologous to the rear cusp of the anterior tooth. The 



