208 I'AL.EOXTOLOCY 



arcli is, that it closely resembles, in the number, shape, and 

 disposition of its bones, the same part in the singular aquatic 

 mammalian quadruped of Australia, called Omitlwrynclms, 

 and Platyims, or duck-mole. The Ichthyosaur, when so 

 visiting the shore either for sleep or procreation, would lie or 

 crawl prostrate, or with its belly resting or dragging on the 

 ground. 



The most extraordinary feature of the head was the enor- 

 mous magnitude of the eye : and from the quantity of light 

 admitted by the expanded pupil, it must have possessed great 

 powers of vision, especially in the dusk. It is not uncommon 

 to find in front of the orbit in fossil skulls, a circular series of 

 petrified thin bony plates, ranged round a central aperture, 

 where the pupil of the eye was placed. The eyes of many 

 fishes are defended by a bony covering consisting of two 

 pieces ; but a compound circle of overlapping plates is now 

 found only in the eyes of turtles, tortoises, lizards, and birds. 

 This curious apparatus of bony plates would aid in protecting 

 the eye-ball from the waves of the sea when the Ichthyosaurus 

 rose to the surface, and from the pressure of the dense element 

 when it dived to great depths ; and they show, writes Dr. 

 Bucldand (Bridgewctter Treatise), " that the enormous eye of 

 which they formed the front, was an optical instrument of 

 varied and prodigious power, enabling the Ichthyosaurus to 

 descry its prey at great or little distances, in the obscurity of 

 night, and in the depths of the sea." 



Of no extinct species are the materials for a complete and 

 exact restoration more abundant and satisfactory than of the 

 Ichthyosaurus; they plainly show that its general external 

 figure must have been that of a huge predatory abdominal 

 fish, with a longer tail and a smaller tail lin ; scaleless, more- 

 over, and covered by a smooth or finely wrinkled skin, analo- 

 gous to thai of the whale tribe. 



The mouth was wide, and the jaws long, and armed with 



