the Fossil Jaws of Stonexjield. 645 



The second part of this system, which occupies the remain- 

 der of the horizontal portion of the jaw, almost as far as the 

 anterior edge of the ascending branch, is formed by a series of 

 seven teeth, of which the posterior are much more closely set 

 than the anterior, without however being absolutely in con- 

 tact ; and are also rather more unequal than in the preceding 

 fragment; the terminal teeth being smaller than the others, 

 and regularly decreasing towards each extremity, beginning 

 from the fourth tooth, which thus forms the principal one. All 

 are, however, of very nearly the same compressed form, pro- 

 vided with two roots, and having the crown but little elevat- 

 ed, compressed, and tricuspid, with the exception of the fifth, 

 in which the terminal points are bilobate, so as to render the 

 crown pentacuspid, with a palmated form. 



Thus by adding one more incisor in front, at the very point 

 of the jaw, and where, in fact, Mr. Broderip even thought he 

 perceived a socket, the number of teeth on one side of the low- 

 er maxilla will be four incisors, one canine and seven molars; 

 and as it appears that the animal to which this fragment be- 

 longed was an adult, Mr. Broderip has arrived at the conclu- 

 sion, that the dentition was the same as that of the opos- 

 sums. But in that case it would differ widely from what has 

 been established with regard to the first fragment; and there- 

 fore Mr. Broderip is of opinion that, as we have already said, 

 it indicates not oidy a different species, but quite a different 

 genus. 



Such are the two fragments on which is founded the belief 

 of the presence of insectivorous marsupials in a formation 

 anterior to the chalk. And having now made ourselves ac- 

 quainted with one of the terms of comparison, let us exa- 

 mine the other, and in fact give a description and sketch of 

 the right maxillary bone of an opossum or of a perameles, 

 which most nearly resembles the fossil jaw. 



The lower jaw of the opossum is narrow, elongated, par- 

 ticularly in its horizontal branch, which is much longer than 

 the ascending one, and somewhat curved lengthwise, and in the 

 same direction both above and below, being considerably at- 

 tenuated in front. 



The vertical portion continues, to a considerable extent, to 

 follow the general curve, like that of a boat, insomuch that 

 the angle of junction is almost effaced; this ascending branch 

 has also a large coronoid process, rounded at the extremity, 

 and considerably hollowed on the outside ; a condyle, trans- 

 verse or rounded, projecting considerably beyond the perpen- 

 dicular line of the coronoid process, and always more or less 

 above the level of the dental line ; and finally, below the 



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