1857.] FALCONER PLAGIAULAX. 265 



crown is little more than one-third of that of it. They are situated 

 both horizontally and vertically in different planes from the premo- 

 lars ; a perpendicular from the acute serrated edge of the latter 

 would coincide with the line of the inner row of the crown-lobes of 

 the true molars, to be described in the sequel, as occurs in the recent 

 Hypsipnjmnus ; and the outline of the coronal surface of the whole 

 molar series would be included within a curve, of which the last 

 premolar formed the most salient part, with a considerable descent 

 on either side of it. 



The crown of the first true molar in Plagiaulax minor (fig. 15, c), 

 which I take first as the more perfect, is of a broad oblong form. 

 Its inner or axial margin supports two well-raised and bluntly conical 

 points or tubercles, separated by a wide cleft, which is parth^ conti- 

 nued down upon the body of the tooth, vertically in a sinus, forming 

 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 

 bevelled 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 anterior 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 indi- 

 cation of any low transverse 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 (fig. 15, d), 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 emi- 

 nences 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 oif at either end, 

 and presenting no marks of composition beyond four or five obscure 

 indications of crenulation, like one of the rows in the tooth of Micro- 

 lestes (see fig. 16). 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, 



u 2 



