FROM THE PURBECK OOLITE. 653 



supial ? secondly, Was it herbivorous ? The general resemblance of 

 the jaws and teeth to those of the living Kangaroo-rats raises at once a 

 strong presumption in favor of the affirmative on both these points. 

 There is, as before noticed, a distinct indication in the fossil of a bend- 

 ing inwards, or*towards the observer, of the posterior inner margin of 

 jaw o, fig. 1 (lower figure), stretching from the anterior boundary of 

 the dentary foramen n. The significance of this character will be ap- 

 preciated by referring to what was said of such an inflection in reference 

 to the Stonesfield Mammalia (p. 311, figs. 379-381). In both spe- 

 cies the true molars are limited to two ; yet the jaw of P. Becklesii 

 was clearly that of an adult, having its full complement of teeth. This 

 is an unexpected number in a quadruped inferred to be marsupial, in 

 which tribe the normal number of molars should be four. In both spe- 

 cies, moreover, the true molars are dwarfed in size, as well as reduced 

 in number. 



In the Kangaroo-rat there is a single grooved pre-molar and four 

 back molars, while in Plagiaulax, the true molars being reduced to 

 two, we find, as if in compensation, three or four grooved pre-molar^l 

 In the pigmy flying opossum of Australia (Acrobata pygmced) there is 

 an analogous development of pre-molars with a reduction of the back 

 grinders to three ; and in the Sub-genus Dromicia, or pigmy phalanger, 

 there are four pre-molars, while the back molars are reduced to three. 

 In the living Myrmecobius* the true molars are greatly in excess of the 

 normal number ; while in the fossil Plagiaulax they are few and rudi- 

 mentary, fewer even than in any of the placental herbivora. It is true 

 that in general form the coronoid (e, fig. 1) of Plagiaulax resembles 

 more that of the predaceous marsupials, and of Dasyurus especially, 

 than of the herbivorous families ; but on the other hand it is less ele- 

 vated, and its surface of less area, than in the predaceous genera, whether 

 marsupial or placental. 



The condyle (d, fig. 1), which is well preserved, is remarkable for its 

 depressed position, — a character which, considered apart from all the 

 rest, might have been taken to indicate a beast of prey ; but it is coun- 

 terbalanced by another peculiarity without example, so far as Dr. Fal- 

 coner is aware, among the predaceous genera, whether marsupial or 

 placental ; viz., the long neck and horizontal projection of the condyle 

 d behind the coronoid e. The other leading indications imply a vege- ■ 

 table feeder ; viz., the limited surface and moderate elevation of the 

 coronoid above the plane of the teeth, the feeble development of the in- 

 flected margin, the absence of a thick angular process, the advanced 

 position of the orifice of the dentary canal (n, fig. 1), and the offset of 

 the inflected margin above it. These characters, taken in conjunction 

 with those of the teeth, would place the Plagiaulax with the vegetable 

 feeders ; and the exceptional position of the condyle may be a special 

 modification, having reference to the abnormal character of the teeth ; 



* A figure of the lower jaw of this quadruped is given in my Principles of 

 Geology, ch. ix. p. 138, 9th ed. 



