PURBECK FORMATIONS. 53 



tooth of this series is a minute premolar {p i) ; the next {p 2) is a larger tooth, showing 

 part of the two fangs above the socket, and the conical subcompressed crown rising 

 rapidly or vertically to the apex of the fore part, and sloping more gradually backward. 

 The third premolar {p 3) shows more equal fore and hind borders of the cone, with an 

 indication of an anterior basal cusp. The crown of the fourth premolar is, as above noted, 

 wanting ; its base was larger than the third, and it probably showed the characteristic 

 height of crown indicated by the dotted line in fig. 1 a of the last (fourth) premolar, as 

 compared with the first true molar. The succeeding seven teeth exemphfy the Stylodont 

 type of true molars ; but the hindmost is here preserved, showing a greater inferiority of 

 height to the penultimate tooth than appears in the type specimen. We have here the signs 

 of individual variation which may have been repeated in generations, as a zoological species. 



Incertee sedis [? Leptocladus duhius\. Plate III, figs. 4, 4 a. 



After repeated scrutiny and comparison I decided to make the specimen about to be 

 described the subject of a lithograph, the ultimate result impressing me with a belief in 

 its having most claim to affinity with Stylodon. It is, however, with diffidence that I 

 offer this remark ; and the fossil is made known rather, or chiefly, as a guide for com- 

 parison with future discoveries of better specimens, which may prove the present to be 

 indicative of a distinct genus and species. 



PI. Ill, figs. 4, and 4 a, magn. 3 diam., represents a left mandibular ramus, with 

 the outer side exposed, wanting the ascending branch, with nine teeth in place, the 

 socket of a canine, and two sockets of incisors. The lower contour is almost straight ; 

 the alveolar one slightly rises along the middle third, and sinks or is concave, but in a 

 very feeble degree, both before and behind. The vertical extent of the ramus is the same 

 behind and before the premolar-molar series. The symphysis curves rather abruptly from 

 below the canine to the incisor-alveoli. The teeth, however, are too much mutilated to 

 yield satisfactory generic characters of the present multidentate Marsupial. 



The crown of the best preserved molar consists of one chief cone, which is high and 

 sharp ; a basal ridge or ' cingulum ' swells into a minute prominence anteriorly, and 

 extends with the base of the crown further back, to form a low hind cusp. The cingulum 

 subsides at the middle of the outer convex part of the base of the main cone, and rises as 

 it recedes therefrom, forward and backward, to form the accessory cusps. The above 

 structure is more or less traceable in the last three teeth in situ, in the present specimens. 

 There is space for one or two such molars between the hindmost and the rising base of 

 the coronoid process. 



The tooth anterior to the foremost of the three molars, by the inferior height of the 

 chief cone in proportion to its breadth, suggests that it may be the last of the premolar 

 series. The minute anterior cusp and the low backward production of the base of the 



