578 Geological Society. 
The characters of the genus Paleosaurus are derived from the 
teeth, which are described as being carinated laterally, and finely ser- 
rated at right angles to the axis. They are stated to differ from those 
of all the Saurians known to the authors: and as the teeth in 
their possession exhibit minor marked characters, they are induced to 
consider that they belonged te two species, which they have named 
P. cylindricum and P., Platyodon. 
The genus Thecodontosaurus is likewise founded on the struc- 
ture of the teeth, and their having been deposited in distinct alveoli. 
Among other remains in the Museum of the Bristol Institution is 
the right ramus of a lower jaw, 34 inches long and 14 in the greatest 
depth, from the summits of the teeth to the under rise, consisting 
of the dental bone, containing 21 teeth, with portions of the sub- 
angular and complementary bones, and perhaps traces of the oper- 
cula. The alveolar groove for the reception of the teeth is formed by 
two ridges of nearly equal height, the teeth being deposited in it, in 
distinct alveoli, to nearly half theirlength. The teeth somewhat re- 
semble in shape a surgeon’s abscess-lancet, being acutely pointed and 
flattened ; while the anterior edge is also curved, but concave and 
strongly serrated, the serrature being directed towards the apex of 
the tooth. The middle teeth are the largest, rising not less than a 
quarter of an inch above the socket. They all possess a conical hol- 
low, and in a specimen belonging to the Rev. D. Williams a young 
tooth is well exhibited in one of the alveolar cavities. From these cha- 
racters the authors infer that the jaw belonged to a Saurian, but not 
to the great genus Lacerta of Linnzus as reformed by Cuvier by re- 
jecting the Crocodiles and Salamanders. They further infer from the 
shape and serrated edge of the teeth that it did not belong to the 
Crocodiles ; nor to the Lizards, whose alveolar inner edge is either 
wanting or much less elevated than the outer. They also show that 
it was not allied to the Monitors, because of the elevated inner alveolar 
edge, the distinct alveoli, the teeth remaining hollow and the 
formation of the new tooth in the same cell with the old one, as well 
as from the great number of the teeth. With respect to the Iguanas 
_ and Scinks they show that the fossil could not have belonged to them, 
in consequence of the distinct alveoli, the inner alveolar edge, and the 
form of the summit and serratures of the teeth: and that it differed 
from the Saurodon in having a ridge on the outside of the tooth with 
the edge crenated and of unequal length. 
Numerous other bones have been discovered, but as none of them 
were found in connexion with teeth, the authors hesitate to assign 
them to either of the genera which they have established. Among 
these remains the following are described : 
Vertebre possessing the peculiar characters, of having the centre of 
the body diminished one half in its transverse and vertical diameters 
so as to resemble an hour-glass; of a suture connecting the annular 
vart or body with the processes ; and in the extremities of the ver- 
tebra being deeply concave. These characters the author conceives 
distinguish the fossil vertebre from those of all recent Saurians. 
A nearly perfect chevron bone; ribs, one flat and imperfect, the 
