154 
DR. MANTELL ON THE FOSSIL REMAINS OF TURTLES. 
surface, and of nearly equal width throughout, with pointed striated extremities, and 
bearing impressions of the horny integument or tortoise-shell — portions of a smooth 
osseous border — and sternal plates with radiated, dentated margins, appear to belong 
to marine Turtles or Chelonia, properly so called. Some specimens of this kind in- 
dicate a total length of thirty-four inches*. 
But the most remarkable form of Testudinata discovered in the Wealden, is one 
allied to the predaceous freshwater Turtles, the Trionyces. It is well known that 
the existing animals of this division of the order have the extremities of the ribs free, 
and not articulated to an osseous border ; and that there are intervals between their 
costal processes, even in the adult state. The external surface of their ribs is covered 
with pits or depressions for the attachment of the soft skin, the only integument with 
which the Trionyces are invested ; and being destitute of scales, their bones exhibit 
no furrows, as in the other genera. But the ribs from Tilgate Forest, while they 
possess the shagreen surface of the recent Trionyces, bear the impress of a scaly 
covering ; and instead of being nearly of an equal width throughout their entire 
length, as in the existing freshwater and marine Turtles, gradually enlarge towards 
the distal extremity, till the outer is nearly twice as wide as the inner termination ; 
a character which obtains only in the ribs of land Tortoises 'f-. The specimens in 
question present, therefore, an assemblage of osteological characters which are not 
found in any known recent species ; and until the discovery of more considerable 
and connected portions of the skeleton, the affinities of the original to existing forms 
cannot be accurately determined. 
In the chalk formation of England, the indications of Testudinata are very rare. 
My collection of cretaceous fossils, which consisted of upwards of ten thousand spe- 
cimens from the South Downs, contained but one certain relic of this order of 
Reptiles ; and I have reason to believe that other collectors have not been more 
fortunate. The Maestricht beds, however, which are referable to the chalk, have long 
been celebrated for the remains of Turtles ; and the ludicrous mistake of Faujas St. 
Fond, who figured and described some bones and sternal plates of a Turtle from St. 
Peter’s mountain, as the antlers of an Elk;}:, led Baron Cuvier to institute a rigorous 
examination of the originals. The result of his inquiry was, that the fossils in ques- 
tion, from the quarries at Maestricht, belong to marine Turtles, differing from any of 
the known recent species 
In the tertiary formations, the remains of Testudinata are common, and most of 
the extinct forms of Chelonia are found in these deposits. The Trionyces, the exist- 
ing species of which are inhabitants of the Nile, Euphrates, and other rivers of warm 
climates, occur fossil in the strata of the Paris Basin, associated with skeletons of 
Palseotheria, &c. 
The tertiary molasse of Switzerland also contains bones of the genera Emys and 
* Fossils of Tilgate Forest, plates vi. vii. f Geology of the South-East of England, p. 255. 
x Hist. Nat. Mont, de St. Pierre, p. 103. § Oss. Foss., tom. v. plate xiv. 
