416 MANUAL OF ZOOLOGY. 



CHAPTER LXV. 

 EXTINCT ORDERS OF REPTILES. 



IT remains now to consider briefly the leading characters of 

 five wholly extinct orders of Reptiles, the peculiarities of which 

 are very extraordinary, and are such as are exhibited by no 

 living forms. 



ORDER V. ICHTHYOPTERYGIA, Owen ( = Ichthyosauria, Hux- 

 ley). The gigantic Saurians forming this order were distin- 

 guished by the following characters : 



The body was fish-like, without any distinct neck, and pro- 

 bably covered with a smooth or wrinkled skin, no horny or 

 bony exoskeleton having been ever discovered. The vertebrae 

 were numerous, deeply biconcave or amphicoelous, and having 

 the neural arches united to the centra by a distinct suture. 

 The anterior trunk-ribs possess bifurcate heads. There is no 

 sacrum, and no sternal ribs or sternum, but clavicles were pre- 

 sent as well as an interclavicle (episternum) ; 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. 163), all exclusively Mesozoic, and 

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

 acteristic of the Lias. There is no doubt whatever but that 

 the IchtkyosauriwSK. 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 

 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- 



