446 MANUAL OF ZOOLOGY. 



sent as well as an interclavicle (epistemum); and false ribs 

 were developed in the walls of the abdomen. The skull had 

 enormous orbits separated by a septum, and an elongated' 

 snout. The eyeball was protected by a ring of bony plates in 

 the sclerotic. The teeth were not lodged in distinct sockets, 

 but in a common alveolar groove. The fore and hind limbs 

 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. 175), all exclusively Mesozoic, and 

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

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

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

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

 boniferous period. There is no doubt whatever but that the 

 Ichthyosauri were essentially marine animals, and they have 

 been oftqn included with the next order (Sauropterygia) in a 

 common grovip, under the name of Enaliosauria or Sea 

 lizards. 



In the biconcave vertebra 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 

 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 ofBuckland, Conybeare, and Owen, the following 

 facts appear to be pretty well estabhshed : — That the Ichthyo- 

 sauri kept chiefly to open waters may be inferred from their 



I^'ig- 175- — Ichthyosaurus communis. 



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 fcre-limbs, and 

 closely resembUng in structure the scapular arcli of the Orni- 



