34 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Nov. 24, 
on the ventral face of the outer condyle, which passes between the 
tibia and the fibula, as in birds. 
11. The tibia is shorter than the femur. Its proximal end is 
produced anteriorly into a strong crest, which is bent outwardly, or 
towards the fibular side. 
12. The astragalus is like that of a bird; and the digits of the pes 
are terminated by strong and curved ungual phalanges. 
The Dinosauria about which we have sufficient information ap- 
pear to me to fall into three natural groups—i. the Megalosauride, 
u. the Scelidosauride, and ii. the [guanodontide. 
i. The Megalosauride. 
1. The maxillary teeth are sharp-pointed, and the crown has a 
longitudinal serrated ridge, either on the middle of its posterior face 
only, or on the middle of its anterior face as well. The serrations 
of the ridge are directed at right angles to the long axis of the 
tooth. The teeth do not become worn by mastication. 
2. The anterior prolongation of the ilium is nearly as large as, 
or larger than, the posterior. 
3. The rami of the mandible are deep and thick and meet by 
rounded ends in the symphysis. 
4. The proximal end of the femur is flattened, curved, and twisted 
in such a manner that its plane is oblique to that of a flat surface on 
which the condyles rest. In other words, it is more or less crocodilian. 
5. There is no dermal armour. 
Teratosaurus, Paleosaurus, Megalosaurus, Poikilopleuron, Lelaps, 
and probably Huskelosaurus belong to this group. 
u, The Scelidosauride. 
1. The maxillary and mandibular teeth have sharp-edged trian- 
gular crowns, with serrated margins, the serrations being oblique to, 
or parallel with, the long axis of the tooth. The teeth are not worn 
down by mastication. 
2. The anterior prolongation of the ilium is more slender than 
the posterior. 
3. The rami of the mandible are slender, and taper to their sym- 
physis. 
4. The proximal end of the femur has a subglobular articular 
head, borne by a neck which is set nearly at right angles to the axis 
of the shaft, while its direction is nearly parallel with a flat surface 
on which the condyles rest. 
5. The integument is (usually) provided with a dermal armour 
in the form of bony scales or spines. 
Thecodontosaurus, Hyleosaurus, Polacanthus (?), and Acanthopholis 
belong to this division. 
il. The Ig quanodontidee. 
1. The maxillary and mandibular teeth have obtuse subtriangu- 
lar crowns; the surface of the enamel being ridged on one or both 
sides. The crowns of the teeth are worn down flat by mastication. 
