80 FOSSIL MAMMALIA OF THE 



is enhanced by a fine serration at the hind half, formed by four fine points of enamel, from 

 which, ridges extend obliquely forward and downward, leaving intervening parallel narrow 

 o-rooves. The height of the crown of the second premolar is rather more than its fore- 

 and-aft breadth. 



In the last premolar {p 4) the increase of size is considerable, as in PI. minor. The 

 two roots are nearly equal, the hind one exceeding. Both swell out slightly before 

 they coalesce and expand into the crown, but the anterior protuberance is most marked. 

 The fore-and-aft extent of this trenchant tooth exceeds its height. The serrate margin 

 is moderately convex. It is formed by eight enamelled points, from each of which 

 a ridge extends obliquely downward and forward, parallel with the course of the four in 

 the antecedent tooth, and to the same extent down the crown ; but both ridges and grooves 

 are more strongly marked in the present premolar. The outer surface of the crown is flat, 

 and slopes at once to the trenchant edge, unbroken save by the oblique ridges on its 

 upper half. The hindmost of these is feeble, and runs below that from the hindmost 

 denticle forming the posterior angle of the crown. There is no trace of the short vertical 

 rising noted in jo 4 of Plagiaulax minor. 



As each specimen is delineated, or outlined, of the natural size, admeasurements are 

 not given in the text. Dividing the length, in a straight line, of the present mandibular 

 ramus, from the apex of the incisor to the back part of the condyle, into nine parts, five 

 of these include the dentition and four the ascending ramus behind the last molar. Of 

 the five parts, including the dentition, a little over four fifths are occupied by the incisor 

 and premolars, and the rest by the two molars. The teeth occupying the four fifths of 

 the dentary tract are expressly and very effectively modified for piercing and cutting : 

 those lodged in the hind fifth of the alveolar tract we may infer, by analogy of other 

 specimens, to have been two small and low tubercular molars adapted for pounding. 



The piercing, holding, and tearing power is limited to one large sub-erect, sub-recurved, 

 laniariform tooth, which by position in the jaw is technically an incisor. The cutting or 

 dividing function is allotted to three teeth, so proportioned and coadjusted as to act as 

 one large carnassial, working by a sub-convexly curved, trenchant, and finely serrate edge, 

 as a shear-blade on a tooth, or aggregate of teeth, of probably like carnassial form or 

 character in the upper jaw. The strengthening oblique ridges and resultant serration of 

 the cutting edge seem well adapted to the division of the tough and dry integument of 

 Saurians. 



The position, shape, direction, and relative size of the condyle, with the size, shape, 

 and duration of the coronoid process, indicate the power and line or direction of work 

 of the mandible, which by the analogy of the Thylacine (fig. 5) and Ursine Dasyure 

 (fig. 20) 1 conclude to have been the work mainly of biting and cutting, with a little 

 crushing or pounding of the divided substances before their final deglutition. The com- 

 parisons, however, with the jaws and teeth of other mammalian species will be deferred 

 till the descriptions of the specimens of Plagiaulax are completed. 



