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LETTER XVIII. 
AMPHIBIOLITHI TORTOISE CROCODILE. 
T he Amphihiolithi form a very large and important class of fossils, 
and of which our own country has produced some very interesting 
specimens. It must, however, be to those of the larger kind that our 
attention must be directed ; since, from their minuteness and extreme 
delicacy, the remains of frogs, serpents, and of the smaller species of 
the genus Lacerta, are very rarely met with, and then can hardly be 
expected to afford us any real instruction. The remarks which I 
shall have to offer will be entirely confined to the Amphibia? reptiles, 
since I know of no decided instance of the mineralized remains of any 
of the A. serpentes. 
The fossil remains of the genus Testudo are rarely found, and 
seldom in such a state as can yield any positive information respecting 
the original animal. Indeed, when we consider that the sections into 
which this genus ( Testudo ) has been divided by Linnaeus, of the sea, 
the fresh water, and the land tortoise, are distinguishable by the feet 
being like fins, or palmated, or club-shaped, with nails, it will be 
seen that any distinction of this kind can rarely be made in the fossil 
remains of these animals ; since, except in the impression in schist, 
which will be presently mentioned, no traces of the feet are, I believe, 
to be found among their fossil remains. 
It may not, however, be improper to observe here, that should any 
remains of this part of these animals be found fossil, they will not 
serve, with certainty, for the distinctions pointed out by this illustrious 
naturalist ; since subsequent discoveries and observations have shown, 
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