Geological Age of Reptiles. — 361 
had a large head, enormous eyes, a short neck, and very long tail ; 
it was furnished with four broad and flat paddles, and was evidently 
destined to live in the sea; it sometimes attained a length of from 
twenty to thirty feet. The Plesiosaurus, which in some respects re- 
sembled the Ichthyosaurus, being also furnished with four paddles, 
but is yet more nearly allied to the Saurians, differs, however, from 
it, and from all other animals, by the extreme length of the neck, 
and the great number of cervical vertebre. The neck of reptiles is 
in general composed of from three to eight cervical vertebra ; and 
even birds (which have the maximum) have but from nine to twenty 
three ; while one species of Plesiosaurus (P. dolichodeirus) has thir- 
ty vertebre. This extraordinary creature, unlike the Ichthyosaurus, 
appears to have been but little calculated to make rapid progress 
through the sea, and was still less fitted for progressive motion on the 
land ; it is therefore probable that it swam on or near the surface of 
the water, carrying its neck like a swan, and darting on its prey, its 
food consisting of fishes, cuttle-fish,&c. Contemporary with the ani- 
mals above mentioned, were several herbivorous reptiles, whose re- 
mains have been found in the lias at Boll, in Wurtemburg, also a spe- 
cies of crocodile ; and at Guildorf, a salamander of enormous size. 
The remains of tortoises and turtles occur also, but very sparingly, 
although, from the foot-marks observable in the red sandstone at 
Corn Cockle Muir, in Dumfriesshire, this family of reptiles must 
have existed at a still earlier period. In this bed also, several spe- 
cies of the Pterodactylus, or flying reptile, first make their appear- 
ance; animals which, with the wings of a bat, and the structure of 
areptile, had jaws furnished with sharp teeth, and claws with long 
ooked nails. i 
The entire series of deposites composing the oolite formation, of 
Which the lias is the inferior, or lower member, abounds with the re- 
mains of the animals of this order, and these are associated with vast 
quantities of marine shells, principally belonging to the ancient mul- 
tilocular genera, namely, Ammonites, Nautilites, Belemnites, &c. 
the whole formation having manifestly been deposited by an ocean. 
The only apparent exceptions to this conclusion are the Stonesfield 
beds, composed of thin strata of calcareous sandy slate, which occur 
in the lower division of the oolite, and contain not only marine plants, 
shells, and bones of reptiles, but also the outer cases or elytra of 
Winged insects, and jaws of animals allied to the opossum, (Didel- 
Phis.) The occurrence of terrestrial mammalia in beds of this an- 
Vou. XXI.—No 2. 46 
