140 ON THE REVOLUTIONS OF 



The third (I. ienuirostris) has slender and pointed teeth, and the 

 muzzle slim and lengthened. 



The fourth (I. intermedins) has teeth of a medium nature hetween 

 the last species and the first. The two latter species do not attain 

 half the size of the two former. 



The jrfesiosaurus, discovered by Mr. Conybeare, must have appeared 

 even more monstrous than the ichthyosaurus. It had similar limbs, 

 but rather more elongated and flexible ; its shoulder and pelvis were 

 stronger, its vertebra? were nearly assimilated to those of lizards ; but 

 what distinguished it from all oviparous and viviparous quadrupeds, 

 was a slender neck as long as its body, composed of thirty vertebra? and 

 upwards, a number greater than that of the neck of all other animals, 

 rising from the trunk like the body of a serpent, and terminated by a 

 very small head, in which are to be found all essential characteristics 

 of those of lizards. 



If any thing could justify those hydras and other monsters which 

 are so often drawn on the monuments of the middle ages, it would 

 assuredly be this plesiosaurus. 



Five species are already known, the most generally distributed (P. 

 dolicliodeirus) is more than twenty feet long. 



A second (P. recentior) found in recent strata, has flatter vertebra?. 



A third (P. carinatus) has a prominence on the lower surface of the 

 vertebra?. 



A fourth, and lastly a fifth (P. pentagonus) and (P. trig onus) have 

 respectively five and three prominences. 



These two genera are everywhere distributed in the lias. They 

 were discovered in England, where the lias is exposed in cliffs of great 

 extent, and they have been also found in France and Germany. 



With them there existed two species of crocodiles, whose bones are 

 also deposited in the lias, amongst ammonites, terebratulae, aud other 

 shells of this ancient sea. We have skeletons of them in our cliffs at 

 Honfleur, where are found the remains from which I have drawn their 

 characters. 



One of the species, the long-nosed gavial, has a muzzle longer and 

 the head sharper than the[gaviai, or long-nosed crocodile of the Ganges; 

 the body of its vertebrae is convex in front, whilst in the crocodiles now 

 existing they are so behind. It has been found in the lias of Franco- 

 nia as well as in those of France. 



A second species, the short-nosed gavial, with a muzzle of mid- 

 dling length, less pointing than that of the gavial of the Ganges, and 

 more so than the crocodiles as now seen in San Domingo. The verte- 

 brae were slightly hollowed at the two extremities. 



