48 FOSSIL MAMMALIA OF THE 



succeeding molars, with slight but progressive increase of height, not of breadth, of 

 crown. The length of the exposed part of the third molar {m 3) is equal to the entire 

 depth of the ramus below the socket : the same may be said of the fourth {m 4) and fifth 

 (;/^ 5) molars ; but the lower border of the jaw may not be fully exposed. 



The crowns of the last two molars {m 6, m 7) are partly broken away ; and those of 

 the last two incisors and first two premolars have suffered mutilation ; otherwise, the 

 whole mandibular series of teeth of Stylodon pusillus is instructively displayed in the present 

 specimen. In comparison with the mandible of Amblotherium soricinum (PI. II, fig. I) it 

 Avell exemplifies the value of the dental characters showing gcHeric distinction in these 

 minute multidentate Marsupials of the Mesozoic period. 



The next example supplies almost as much of the dental series of the upper jaw, as 

 does the foregoing specimen of that of the lower jaw. The grounds for referring the 

 specimen (PI. II, figs. 14 and 14 a) to Stylodon pusillus will be given, as might be looked 

 for, in some detail. 



In the existing Insectivores which show teeth, or at least the molar series of teeth, 

 resembling those of certain species of smaU Mammals represented by fossil jaws and teeth 

 from the Purbeck marl-beds, the longest and largest lobe or cusp projects from the inner 

 part of the crown in the upper molars, from the outer part in the lower ones. This is 

 well shown in Chrysoddoris} in which the inside view of the upper teeth and the outside 

 view of the lower teeth present the form or character of crown closely resembling the type 

 of that which suggested the generic name Stylodon. Somewhat of the same character is 

 seen in the Tenrecs {Centetes)^ which more nearly resemble Stylodon in the proportions of 

 the incisors and canine. In Perameles^ and Didelpliys^ also, the longest cusps of the true 

 molars project from the inner half or side of the crown in the upper jaw, and the reverse 

 in the lower jaw. The tendency to adhere to this reversing of position, as it seems, of upper 

 and lower molars in respect to outer and inner side-configuration of crown is discernible 

 in the teeth of Sarcophilus ursinus, PI. II, fig. 3 c, and fig. 4 c. 



Upon these considerations, and after close and repeated scrutiny of the teeth, which a 

 successful application of the needle-point has exposed in one of Mr. Beckles' slabs, affording, 

 at first sight, small promise of such result, I conclude them to belong to the upper jaw. 



The apparent continuation of the jaw-bone {a, h, fig. 14 a) directly down, or vertically, 

 from the alveolar margin of this specimen, at first suggested a mandibular character. But 

 the cracks and fissures (ib. a, a) close to that margin, and the thinness of the osseous plate 



^ Fr. Cuvier, genre Chrysoclore, 'Annales du Museum d'Histoire Naturelle,' torn, xii (1808), p. 49, 

 pi. iii, figs. 1 — 5. Ib., 'Dents de Mammif^res,' Bvo, 1825, p. 63, pi., no. 18. (The line-engraving in 

 the original memoir is better than the lithograph in the subsequent work.) 



2 lb., p. 46 ; and ib., p. 69, pi. no. 19. 



^ lb., p. 71, pi. no. 23, a. 



4 lb., p. 73, pi. no. 23, c. 



