26 GEOLOGICAL SURVEY 
with the scutes, but in marine species they only abut against them. The bones of the extremities 
are solid, and the humerus much curved. The clavicles, which are in number two on each side, 
are united with the scapula, so as to produce a bone somewhat resembling a tripod. 
The peculiarity in the articular surface of the vertebra of serpents that distinguishes them from 
other reptiles, is an oblong concavity, placed with its longer diameter transversely with the axis of 
the spinal column. 
Few subjects have excited equal interest among Paleontologists, with the discovery of the extra- 
ordinary forms of this class found in the secondary rocks of Europe. Their gigantic dimensions 
and their anomalous structure, which offered but few points of comparison with living forms, were 
well calculated to excite wonder, if not incredulity, as to their real character. These have been 
studied with great success by British naturalists, and they have recently been marshalled into their 
appropriate places in the scale of being, by Professor Owen, in a most valuable report on British 
fossi] Reptilia. 
They are distributed under the following orders in that report. 
Orders of Fossil Reptilia. 
1. Order—Enaliosauria, 5. Order—Pterosauria, 
2. Order—Crocodilia, 6. Order—Chelonia, 
3. Order—Dinosauria, 7. Order—Ophidia, 
4, Order—Lacertilia, 8. Order—Batrachia. 
Characters of the Orders.—The Enaliosaurians, at the same time that they present in their 
structure true typical reptilian characters, such as the unanchylosed state of the cranial, lower 
maxillary and vertebral elements, they also, by other characters, approach the cetacea. For, 
besides having nostrils near the top of the head, for breathing, their fore and hind paddles resemble, 
externally, those of certain cetacea; and it is from this modification of the reptilian type that they 
derive the name of Enaliosarus, or marine Saurians. Other reptiles have extremities adapted to a 
life on land, or they are fitted for both land and water—these were exclusively aquatic. 
The remarkable genera Ichthyosaurus and Plesiosaurus, constitute, according to Professor 
Owen’s arrangement, the first order; and certainly their huge dimensions and anomalous structure 
entitle them to a separate and distinguished place at the head of the reptiles. 
Icthyosaurus.—The head of this reptile in form resembled that of the porpoise, with compar- 
atively less space for brain, but was of gigantic dimensions; a head figured by Dr. Buckland 
measures over four feet in length. The eyes must have been of enormous size, for the orbital 
cavity in one instance was found to be fourteen inches in diameter. The lower maxille are com- 
posed of several bones, like those of Reptilia. 'The teeth, which are conical and striated, are not 
inserted in distinct sockets, but in a continuous groove, which presents, however, rudimentary divi- 
sional plates at the bottom and sides of the groove, extending between the teeth. The mode of 
growth of the teeth is very similar to that in the alligator; the young tooth pressing against the 
basal margin produces a notch in the old tooth. 
The vertebre, instead of the concavo-convex articular surfaces of reptilian vertebrae, present 
conical cavities, like those in the osseous fishes. "The diameters of the vertebrae, in the direction 
of the spinal column, or their anterio-posterior diameter, is quite small, and they are consequently 
flat, compared with those of osseous fishes. 
