Triassic deposits.
Thus there are various deposits in different regions which have
yielded the remains of Reptiles, and which cannot in the meanwhile
be definitely referred either to the Permian series or to the
Trias by clear stratigraphical or palaeontological evidence. All
that can be done in such cases is to be guided by the characters
of the Reptiles themselves, and to judge by their affinities to
remains from known Triassic or Permian rocks to which of these
formations the beds containing them should be referred; but it
is obvious that this method of procedure is seriously liable
to lead to error. In accordance, however, with this, the only
available mode of determination in some cases, the remains of
_Thecodontosaurus_ and _Palaeosaurus_ discovered in the dolomitic
conglomerates near Bristol will be considered as Triassic, thus
leaving _Protorosaurus_[20] as the principal and most important
representative of the Permian Reptiles.[21] The type-species of
the genus _Protorusaurus_ is the _P. Speneri_(fig. 138) of the
"Kupfer-schiefer" of Thuringia, but other allied species have
been detected in the Middle Permian of Germany and the north
of England. This Reptile attained a length of from three to four
feet; and it has been generally referred to the group of the
Lizards (_Lacertilia_), to which it is most nearly allied in
its general structure, at the same time that it differs from
all existing members of this group in the fact that its numerous
conical and pointed teeth were implanted in distinct sockets in
the jaws--this being a Crocodilian character. In other respects,
however, _Protorosaurus_ approximates closely to the living Monitors
(_Varanidoe_); and the fact that the bodies of the vertebrae are
slightly cupped or hollowed out at the ends would lead to the
belief that the animal was aquatic in its habits. At the same
time, the structure of the hind-limbs and their bony supports
proves clearly that it must have also possessed the power of
progression upon the land. Various other Reptilian bones have
been described from the Permian formation, of which some are
probably really referable to Labyrinthodonts, whilst others are
regarded by Professor Owen as referable to the order of the
"Theriodonts," in which the teeth are implanted in sockets, and
resemble those of carnivorous quadrupeds in consisting of three
groups in each jaw (namely, incisors, canines, and molars). Lastly,
in red sandstones of Permian age