36 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Nov. 24, 
—I. The Dinosauria, with the cervical vertebree relatively short, and 
the femur as long as, or longer than the tibia. II. The Compso- 
gnatha, with the cervical vertebre relatively long, and the femur 
shorter than the tibia. 
3. The affinities of the ORNITHOSCELIDA with other Reptiles. 
If we consider the relations of the Ornithosauria to other rep- 
tiles, it is at once obvious that they belong to that great division of 
the class in which the thoracic vertebree have distinct capitular and 
tubercular processes, the latter being longer than the former, and 
springing from the arch of the vertebrx, as in the crocodiles. These 
reptiles may be termed Suchospondyla, to distinguish them from 
another great group, in which the thoracic vertebrae have the capi- 
tular and tubercular processes fused together into one process or 
facet, and which may be termed the Hrpetospondylia,—trom a third, 
in which the capitular and tubercular processes are both mere tuber- 
cles springing from the centrum of the thoracic vertebrae, Perospon- 
dylia,—and from a fourth, Pleurospondylia, in which the thoracic 
vertebre have neither capitular nor tubercular transverse processes, 
but the ribs are sessile upon, and fixed to, the vertebree. 
The last-named group consists of the Chelonia ; the Perospondyla 
contain only the Ichthyosauria ; the Erpetospondylia comprise the 
Ophidia, Lacertilia, and Plesiosauria; while the Suchospondyla 
embrace the Crocodilia, the Dicynodontia, the Pterosauria, and the 
Ormithoscelida. 
The closest relations of the Ornithoscelida within this group are 
with the Dicynodontia on the one hand, and the Crocodilia on the 
other. The sacrum and the iliae bones of the Dicynodonts more 
closely resemble the corresponding parts of the Ornithoscelida than 
they do those of any other Reptilia, except the Pterosauria* ; and 
there are a good many points of resemblance in the skull and denti- 
tion. Our knowledge of Rhopalodon and of Galesaurus is hardly 
sufficient to afford grounds for a safe opinion; but it seems probable 
that they will turn out to be annectent forms between the Dicyno- 
dontia and the Ornithoscelida. 
The connexion of the Crocodilia with the Ornithoscelida is proba- 
bly to be sought in some common form, more Lacertilian in its cha- 
racter than any of the known members of either of these groups. 
The oldest known Crocodilians, Belodon and its congeners, exhibit 
modifications which approximate them rather to the Lacertilia than 
to the Ornithoscelida. 
If we seek for reptilian allies of the Ornithoscelida in formations 
of older date than the Trias, the Permian forms alone present them- 
selves. Our knowledge of these is almost entirely due to the re- 
searches of Von Meyer, the results of whose investigations have 
hardly received the attention they deserve. They prove the exist- 
ence of two very distinct reptilian genera, Proterosaurust and Para- 
* The complete occlusion of the obturator foramen by bone occurs in both the 
Dicynodontia and the Pterosauria, and in these alone among Reptiles. 
+ The generic distinctness of Aphelosaurus of Gervais appears to me to be 
doubtful. 
