450 PORTION OF AN OPOSSUM'S JAW 



London Clay. London Clay. 



I was much disappointed in this last visit to the quarry to 

 find that the stratum of sand in which the fossils are found 

 was not exposed, owing to its lying below the clay, and the 

 small quantity required in manufacturing the bricks. Some 

 of the sand however had been laid aside, and was being sifted 

 by a daughter of one of the workmen, who picked out the 

 sharks' teeth, which, with about three or four per cent, of 

 fine shingle, formed the residuum. The teeth were plentiful 

 enough, but I could not detect the slightest fragment of a 

 shell. The foreman told me that they had sunk about ten 

 feet into the sand, without passing through it. It would be 

 desirable to ascertain at what depth the chalk is there met 

 with, but this point I had not the means of determining : 

 probably it is not far below the surface, and this sand may 

 perhaps separate the chalk from the overlying clay. 



Upon my calling on Mr. Colchester, I found that he had 

 been so fortunate as to have added to his previous discoveries 

 that of the interesting fragment represented at fig. 60, con- 



fa) Portion of the lower jaw of the fossil Opossum, enlarged one half, 

 (ft) View of the crown of the tooth, twice the natural size ; (seen from within). 



sisting of a portion of the right ramus of the lower jaw of an 

 opossum, in which one of the false molars is happily retain- 

 ed. The tooth in its symmetrical form, united with the in- 

 dication of an anterior as well as posterior heel or talon, does 

 not agree with any species of didelph with which I have as 

 yet been able to compare it, but I think no doubt can be en- 

 tertained of the generic or family affinities indicated by the 

 characters which it exhibits. Judging from the empty alve- 

 oli on either side, the tooth appears to be the one immediate- 

 ly succeeding the true molars : its posterior tubercle is 

 strongly developed, and divided longitudinally by a prominent 

 ridge, the continuation of which forms the posterior edge of 

 the body of the tooth. At the base of the anterior root of 

 the tooth the opening of & for amen is seen, on the outer surface 

 of the bone. 



