found at Kyson in Suffolk. 193 



to the corresponding part of the Opossums as to warrant the 

 expectation that subsequent discoveries may prove the differ- 

 ences above-mentioned to be merely specific. The crown of 

 the spurious molars of the placental Ferae which present the 

 same general form as the fossil,, are thicker from side to side 

 in proportion to their breadth ; the spurious molars of the 

 Dasyurus Thylacinus and Phascogale differ in like manner 

 from the fossil. It is in the marsupial genera Didelphys and 

 Perameles that the false molars present the same laterally 

 compressed shape as in the fossil. Now besides the Fig. 2, a. 

 perfect tooth, the fossil includes the empty sockets of 

 two other teeth (fig. 2, b) ; and the relative position of 

 these sockets places the Perameles out of the pale of 

 comparison. On the hypothesis that the present 

 fossil represents a species of Didelphys, the tooth in Nat. size. 

 situ unquestionabty corresponds with the second or middle 

 false molar, right side, lower jaw. This is proved by the size 

 and position of the anterior alveolus. Had the tooth in situ 

 been the one immediately preceding the true molars, the 

 socket anterior to it should have been at least of equal size, 

 and in juxta-position with the one containing the tooth. The 

 anterior socket, however, is little more than half the size of 

 the one in which the tooth is lodged : it is also separated from 

 that socket by an interspace equal to that Fi g .2,c. 



which separates the first from the second false 

 molar in the Didelphys Virginiana. This is 

 well shown in the inside view (fig. 2, c). In the 

 placental mammalia, in which the first small 

 false molar is similarly separated by a dia- inside. Nat. size. 

 sterna from the second, the first false molar has only a single 

 fang. In the present fossil the empty socket of the first false 

 molar proves that that tooth had two fangs as in the marsupial 

 Ferae and Insectivora. There is nothing in the size or form of 

 the socket posterior to the implanted tooth of the fossil to 

 forbid the supposition that it contained a spurious molar re- 

 sembling the one in place ; had it been the socket of a true 

 molar, as Mr. Charlesworth conjectures, then the fossil could 

 not have belonged to Didelphys or to any other known marsupial 

 genus, because no known marsupial animal which presents the 

 Ann. Nat. Hist. Vol.4. No. 23. Nov. 1839. p 



