214 



CHAPTER XXXV. 



EXTINCT ORDERS OF REPTILES. 



It remains now to consider liriefly the leading characters of 

 six wholly extinct orders of Ileptiles, the peculiarities of 

 which are very extraordinary, and are such as are exhibited 

 by no living forms. 



Order V. Ichthyopterygia, Owen { = I(Mk7josaurm, Hux- 

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

 guished by the following characters : — 



The hody was fish-like, ivithout any distinct neck, and proh- 

 ably covered with a smooth or ivri7ikled skin, no horny or bony 

 exoskeleton having been ever discovered. The vertchw iverc mi- 

 merous, deeply biconcave or aniphiccelous, and having the neural 

 arches united to the centra by a distinct sicture. The anterior 

 trunk-ribs possess bifurcate heads. There is no sacrum, and no 

 sternal ribs or sternum, but clavicles tvere present as well as an 

 interclavicle (episternum) ; and false ribs were developed in the 

 walls of the abdomen. The skidl had enormous orbits separated 

 by a septum, and an elongated snout. The eyeball ivas pro- 

 tected by a ring of bony plates m the sclerotic. The teeth were 

 not lodged in distinct sockets, but in a common alveolar groove. 

 The fore and hind limbs were converted into sioimming-imddles, 

 the ordinary number of digits {five) reinaining recognisable, but 

 the phalanges being greatly increased in number, and marginal 

 ossicles being added as well. A vertical caudal fin loas in all 

 probcdiility present. 



The order Ichthyopterygia includes only the gigantic and 

 fish-like Ichthyosauri (fig. 564), all exclusively Mesozoic, 



