452 
The length, thickness, and indications of condyles in the femur, 
and the length, thickness, and angular form of the metatarsal bones, 
place, he says, the Plesiosaurus and the Ichthyosaurus’ out of the 
pale of comparison ; as well as the Mosasaurus, the locomotive ex- 
tremities of which are considered to have been flattened paddles. 
The superior expanse of the pubis and the broad coracoid (?), with 
the form of the femur and the gigantic proportions of the bones, for- 
bid a reference to any subgenera, recent or extinct, of the crocodilian 
reptiles ; and he shows that it is distinct from the Poikilopleuron of 
M. Deslongchamp by the long bones of that Saurian having medul- 
lary cavities. 
Saurian Teeth from the Lower Greensand.—These teeth, described 
by Mr. Owen in his ‘ Odontography’ under the name of Polypty- 
chodon, are characterized by the crown presenting numerous closely 
set longitudinal ridges, which are continued, of nearly equal length, 
to near the apex of the crown. In their size and simple conical form 
the teeth of the Polyptychodon resemble those of the great sauroid 
fish, Hypsodon, Ag. , but may be distinguished by the solid compact 
structure of the dentine, which is resolved by decomposition into 
successive cones ; and also by the ridges on the exterior of the crown 
of the Hypsodon’s teeth being alternately long and short, and ter- 
minating abruptly at different distances from the base, the interspaces 
between the longer ridges widening as they approach the apex. ‘The 
tooth of the Polyptychodon is slightly and regularly curved, and in- 
vested with a layer of enamel of a clear, amber-brown colour, and of 
which the ridges are composed, the surface of the outermost layer 
of dentine being smooth. A tooth from the lower greensand near 
Maidstone has’a crown three inches long, and one inch four lines 
across the base. It consists of a body of compact dentine composed 
of successive lamelliform cones, and has a short and wide conical 
cavity at the base. 
From the teeth supposed to have belonged to the Poikilopleuron, 
the specimens above described differ in the ridges on the crown 
being greater in number and more closely set, as well as in the form 
of the teeth being nearly circular instead of elliptical; fromthe teeth 
of the Pliosaurus they differ also in being round and not three-sided, 
and in having longitudinal ridges over the whole surface of the crown ; 
and from the teeth of the Mosasaurus they differ in being ridged 
and not smooth. 
In conclusion, Mr. Owen states, that as the Hythe Saurian is di- 
stinct from all other described Saurians, and as these teeth belonged 
to a great Saurian also undescribed, and further, as the Maidstone 
tooth was found in the same formation as the Hythe fossil, so it may 
be convenient to consider all these remains for the present to have 
belonged to the genus Polyptychodon, originally ie for the 
animal which was provided with the teeth. 
