472 MANUAL OF ZOOLOGY. 



were converted into swimming-paddles, the ordinary number 

 of digits (five) remaining recognisable, but the phalanges being 

 greatly increased in number, and marginal ossicles being added 

 as well. A vertical caudal fin was in all probability present. 



The order Ichthyopterygia includes only the gigantic and 

 fish-like Ichthyosauri (fig. 205), all exclusively Mesozoic, and 

 abounding in the Lias, Oolites, and Chalk, but especially char- 

 acteristic of the Lias. If, however, the Eosaurus Acadiensis 

 (Marsh) of the Coal-measures of Nova Scotia be rightly re- 

 ferred to this order, then the Ichthyopterygia date from the Car- 

 boniferous period. There is no doubt whatever but that the 

 Ichthyosauri were essentially marine animals, and they have 

 been often included with the next order (Sauropterygia] in a 

 common group, under the name of Enaliosauria or Sea- 

 lizards. 



In the biconcave vertebrae and probable presence of a ver- 

 tical tail-fin, the Ichthyosaurus approaches the true fishes. 

 There is, however, no doubt as to the fact that the animal was 

 strictly an air-breather, and its reptilian characters cannot be 



Fig. lo*,. Ichthyosaurus communis. 



questioned, at the same time that the conformation of the limbs 

 is decidedly Cetacean in many respects. Much has been 

 gathered from various sources as to the habits of the Ichthyo- 

 saurus, and its history is one of great interest. From the re- 

 searches of Buckland, Conybeare, and Owen, the following 

 facts appear to be pretty well established : That the Ichthyo- 

 sauri kept chiefly to open waters may be inferred from their 

 strong and well-developed swimming-apparatus. That they 

 occasionally had recourse to the shore, and crawled upon the 

 beach, may be safely inferred from the presence of a strong 

 and well-developed bony arch, supporting the fore-limbs, and 

 closely resembling in structure the scapular arch of the Orni- 

 thorhynchus or Duck-mole of Australia. That they lived in 

 stormy seas, or were in the habit of diving to considerable 

 depths, is shown by the presence of a ring of bony plates in the 

 sclerotic, protecting the eye from injury or pressure. That 

 they possessed extraordinary powers of vision, especially in the 

 dusk, is certain from the size of the pupil, and from the enor- 



