182 Mr Mantell on the Geological Age ()f Reptiles. 



sures ; the remains of Monitors having been found in the bitu- 

 minous slate of Thuringia ; and those of a crocodile in the gyp- 

 seous red sandstone of England : but it is not till we arrive at 

 the Lias that the remains of reptiles occur in any considerable 

 quantity. At that period the earth must have teemed with ovi- 

 parous quadrupeds ; and the enaliosauri, or those which inha- 

 bited the sea, appear to have been equally numerous with those 

 of the land and rivers. The prodigious quantity of the remains 

 of these animals which has, within a comparatively short period, 

 been found in England alone, is truly astonishing ; and if to 

 these we add the immense numbers that have been discovered 

 in France, Germany, &c., and reflect that for one individual 

 found in a fossil state, thousands must have been devoured or 

 decomposed ; and that even of those that are fossilized, the num- 

 ber that comes under the notice of the naturalist must be" trif- 

 ling compared with the quantities unobserved or destroyed by 

 the labourers, we shall have a faint idea of the myriads of 

 "creeping things''' which inhabited the ancient world. 



In England, the lias contains more especially the remains of 

 two extinct marine genera, the Ichthyosaurus (fish-like lizard), 

 and Plesiosaurus (animal resembling a lizard), whose osteology 

 is most extraordinary, combining characters observable in the 

 cetacea, fishes, and saurians, but yet decidedly belonging to the 

 order of Reptiles. The Ichthyosaurus, of which several species 

 have been discovered, 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 resembled the Ich- 

 thyosaurus, 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 vertebrse. The neck of reptiles is 

 in general composed of from three to eight cervical vertebras ; 

 and even birds (which have the maximum) have but from nine 

 to twenty-three ; while one species of Plesiosaurus (P. dolicho- 

 deirus) has thirty vertebrae. This extraordinary creature, un- 

 like the Ichthyosaurus, appears to have been but little calcu- 

 lated to make rapid progress through the sea, and was still less 



