AND CLASSIFICATION OF THE FOSSIL RFPTJLIA. 
281 
ossification, wliicli has been lost. (Jther fragments of long bones appear to be 
referable to the fibula, bi;t they are too imperfect for determination without re-exarni- 
nation of the specimens. There is, therefore, no doubt that Britliopus, if all these 
bones are correctly referred to it, behmgs to the Anomodont oixler, and that its place 
is substantially that assigned to it, by Sir IT. Owen. TTiere is also good reason 
for accepting the conclusion that Deuterosaurvs and Bhopalodon must be closely 
associated with it, and they contribute materially to a knowledge of the vertebral 
column and limb bones of the group. But I should place them in the sub-order 
Gennetotheria. 
I have seen no evidence v/hich establishes generic identity between the Anomodonts 
from the Triassic rocks of India and the Dicynodonts from South Africa. 
Comparison ivith Placodus. (See Plate 24, figs.* 5, G.) 
In Placodus the malar succeeds the maxillary, and behind the orbit overlaps the 
squamosal, which is equally deep and is prolonged backward, forming the outer bar 
of the temporal foss. The relation of the squa.mosal to the expanded plate of the 
back of the skull is that of an Anomodont, for the back of the skull in Placodus is a 
basin-shaped space. The quadrate bones descend below the squamosals at the outer 
limits of the basin, but, except at the margin of the condyle, which articulates with 
the lower jaw, the bone is not exposed in lateral view. Below the squamosal is a 
bone which is in the position of the supra-quadrate and quadrato-jugal, and it 
appears to be divided by an oblique suture which would separate the transverse 
supra-quadrate part from the vertical quadrate part or quadrato-jugal. There is a 
sub-circular excavation at the anterior angle where these parts meet, and this con¬ 
cavity, which is probably auditory, forms the posterior and inferior limit of the 
compressed vertical temporal arch. 
The mode of union of the head with the vertebrae was remarkable. Placodus 
shows no sign of a basi-occipital condylar articulation, for the inferior margin of the 
foramen magnum is a thin film of bone. But, laterally, on each side of the middle of 
the foramen magnum, the ex-occipital bones are prolonged outward and backward, 
exactly like the posterior zygapophyses of a vertebra ; and on the left side, which 
alone is disengaged from the matrix, this process shows on its inferior surface a 
transversely oblong fiat facet, which looks downward. This is the occipital condyle ; 
and thus Placodus has two occipital condyles, which closely approach to the 
Mammalian type, and the neural arch of the atlas, and not the centrum, articulates 
with the skull so far as the evidence goes. Therefore I am led to compare the 
Placodontia and Cotylosauria, and to infer that they are probably members of the 
same group of animals. Since the Mammalian atlas unites with the skull, by 
elements of the neural arch, and the centrum takes no part in the articulation, we 
seem to find in Placodus a Beptile in which the mode of union of the vertebral 
2 O 
MDCCCLXXXIX. — B. 
