714 PKOF. OWEN ON THE RANK AND AFFINITIES rx 



measurements given by Prof. Cope of a dorsal vertebra of his 

 Clidastes planifrons, which he calls " a large species," is in favour of 

 the quaternary lizard : — 



Admeasurements of Trunk -vertebra. 



Clidastes. Megalania. Palceophis. 



Length of a median dorsal centrum 0*072 0*090 0032 



Width of the ball of a median dorsal centrum... 0*048 0*060 0010 



Depth „ „ „ „ „ ... 0040 0048 0009 



Megalania, like Amblyrhynchus, may have been a lizard of 

 aquatic habits ; but evidence of the limbs has not yet been obtained. 



Thus Mosasaurus, as a Lacertian, is represented by a successor of 

 similar dimensions ; as an Ophidian it has shrunk to the insignifi- 

 cant proportions indicated in the preceding Table, unless the " great 

 sea-serpent " of our newspapers should establish its claims for 

 admittance into the scientific catalogue. 



But size, of course, is no criterion of affinity ; and if a marine 

 animal, scientifically entitled to be called "serpent" should be 

 discovered of a size surpassing the hugest Mosasaur, it would not 

 affect the Cuvierian determination of the great Sea-lizard of the 

 Cretaceous period. 



To what are such forms as the Pliosaur and Geosaur tending or 

 pointing, from their upper Jurassic scene of life ? To the special 

 Ophidian or the special Lacertian modification of their cold-blooded 

 class ? 



Hardly to the Serpents ; for these are themselves plainly modi- 

 fications of an already specialized Lacertian group ; they are a 

 still more specialized offshoot from the common Saurian stem. "We 

 trace the transition, or recognize signs of such passage in Pseudopus, 

 Anguis, &c. 



The nearest of kin to the Geosaurus of the Lower Kimmeridge 

 of Monheim, and to the Leiodon of the Upper Kimmeridge or Port- 

 landian Marls of Portel, are the Mosasaurians of the Chalk. 



These Reptiles plainly mark a progress to a more specialized 

 Saurian type, which prevails in the present life-world under the 

 manifold modifications of the great Lacertian order. 



While retaining the marine habits and mode of motion of the 

 Pliosaurs and Polyptychodonts, the Mosasaurians show not a single 

 step toward the further and extremer modifications exemplified in 

 the probably marine and unequivocal Ophidian genera of the Eocene 

 period. 



To call the Maestricht reptile a " Pythonomorph " is to raise a 

 delusive beacon, misguiding the voyager in the discovery of the true 

 course of organic change. When the Mosasaurians "tempested the 

 ocean " the time of the sea-snakes had not yet come. 



Professor Cope, rejecting the determination deduced from the 

 facts submitted, affirms (after a summary of the characters which he 

 ascribes to fche osseous and denial systems of his Pythonomorpha) 



