28 GEOLOGICAL: SURVEY 
still further from the latter, by being striated on the sides of the crown. And the teeth of the 
Gavial are compressed in an opposite direction. 
Goniopholis crassidens.—The teeth of this species have thick, round blunt crowns, finely striated, 
and marked by two strong ridges which extend to the termination of the enamel. 
The other genera belonging to the group, with biconcave vertebra, are— 
Teleosaurus, Streptospondylus, 
Steneosaurus, Cetiosaurus. 
Poikilopleuron. 
Dinosauria.—The fossils of this order are characterised by a large and unusual sacrum, com- 
posed of five anchylosed vertebra, by the great height and breadth of the neurapophyses, and by 
having the ribs articulated at the anterior portion of the spine by a head and tuburele, and to the 
rest of the spinal column by a head attached to the transverse process only. ‘They were all of 
gigantic size—far exceeding, in this respect, all living reptiles. ‘The Megalosaurus must have been, 
according to Prof. Owen’s determination, full thirty feet in length. The [guanodon was fifteen feet 
long, while his ‘living relative, the Iguana of the West Indies, seldom attains a length of five feet, 
even with the addition of a long prehensile tail, which could not have belonged to the Iguanodon. 
Lacertilia—The animals whose fossil remains are included under this order approach in struc- 
ture the living lizards, which have compressed angular teeth, with the edges denticulate : in some 
recent species there is an additional row on the posterior edge of the palate. 
The fossil species deviate very widely from any living types. Prof. Owen has designated the 
mode in which the teeth are attached to the jaw, by the term acrodont, when they are anchylosed 
to the summit of an alveolar ridge; plewrodont, when they are attached to the bottom of an 
alveolar groove ; and ¢hecodont, when inserted loosely in sockets, or anchylosed to the walls of the 
alveoli. ; 
The following genera are placed here. 
Mososaurus, Rhyncosaurus, 
Leiodon, 'Thecodontosaurus, 
Rhaphiosaurus, Paleosaurus, 
Lacerta, Cladeiodon, 
Pierosauria.—The anomalous character of the remains placed in this order is made quite 
evident by the widely differing conclusions of distinguished naturalists respecting them—the Ptero- 
dactyle having been referred to birds and Mammalia respectively. Cuvier was the first to settle 
the true affinities of this strange animal, having apparently the head and neck of a bird joined to 
the wings of a bat. He shewed that however great the resemblance to these animals may appear, 
the differences were still greater. No bird has more than one metatarsal bone—in the Pterodactyle 
they are as numerous as the phalanges. No bird has less than nine cervical vertebre—the Ptero- 
dactyle has only six or seven: and no Mammal has so small a cranium in proportion to the beak. 
Besides, the teeth are truly saurian. It was a critical examination of such characters that enabled 
Cuvier to refer this animal to the saurians. 
Prof. Owen has added, with a doubt, two other genera to this order. 
Pterodactyle, Polyptychodon, Rysosteus. 
