440 



PLAGIAULAX. 



inferior premolars are reduced to a single, but enormously 

 large and massive, carnassial, with two small tubercular 

 teeth behind it. The carnassial (Plate XXXIV. figs. 9—12) 

 consists of a long blade, high in front and lower behind, so 

 that, if notched in the middle, the divisions would in some 

 degree resemble the anterior and posterior lobes of the corre- 

 sponding tooth in the placental Carnivora ; ! and the worn 

 summit is distinctly concave lengthwise ; conversely, in both 

 species of Plagiaulax the corresponding tooth is convex, and 

 the outline of the whole series describes a convex curve, of 

 which the last premolar forms the most salient part. The 

 base of the carnassial in Thylacoleo is ' slightly grooved ver- 

 tically' on the inside (fig. 9). These indentations disappear 

 about half-way up towards the edge, where the surface be- 

 comes reticulately rugose, being precisely the reverse of 

 what occurs in the last premolar of Hypsiprymnus and 

 Plagiaulax. Besides the difference of their position upon 

 the teeth, the grooves of the carnassial of Thylacoleo present 

 the appearance of furrows, separating superficial undulations 

 of the enamel. A transverse section of the basal part of the 

 crown would yield a faintly crenated outline, wholly different 

 from the salient and re-entering angles of the close-set 

 parallel grooves of Plagiaulax and Hypsiprymnus. These 

 undulations are exhibited chiefly, if not solely, on the inner 

 side ; their presence on the outer is not mentioned. Further, 

 if the indentations on the premolar of Thylacoleo are to count 

 for anything as significant of affinity, it should be with 

 Hypsiprymnus rather than with Plagiaulax, since the furrows 

 are vertical in the two former. In fact, in the outline and 

 proportions of the vertical section, the premolar of Thylacoleo 

 differs less from Hypsiprymnus than it does from that of 

 Plagiaulax. I have failed to realize the asserted resemblance 

 between Plagiaulax and Thylacoleo in the form of the last pre- 

 molars ; and in the details of outline, section, curvature of 

 edge, crenulation, surface-markings, &c, I am more impressed 

 with the differences than with any one point of agreement. 



Let us now consider the inference as to the function of 

 these teeth. It is expressed thus : — ' The large front tooth 

 is formed to pierce, retain, and kill ; the succeeding teeth 

 are like the blades of shears, adapted to cut and divide soft 

 substances like flesh,' &c. Professor Owen has elsewhere 

 described the premolar of Hypsiprymnus as trenchant, 2 and I 

 have shown above that the tooth is essentially alike in 



1 ' The first molar is lunate, the cusps and a slight, ridge passing to a small 



turning inwards, and the anterior cusp depressed posterior cusp.' — Stutchbury, 



rising at a salient angle ; the edge is loc. cit. 



trenchant outwards ; the second molar is 2 Odontography, vol. i. p. 389. 

 triangular with a large anterior cusp, 



