VERTEBRATA: REPTILIA. 559 



CHAPTER LXII. 

 EXTINCT ORDERS OF REPTILES. 



IT remains now to consider briefly the leading characters of 

 six 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 prob- 

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

 exo skeleton having been ever discovered. The vertebra were nu- 

 merous, deeply biconcave or amphicozlous, 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 present 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 (fig. 313). 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, or principally, the 

 gigantic and fish -like Ichthyosauri (fig. 311), all exclusively 



Fig. 311. Ichthyosaurus cominunis. 



Mesozoic, and abounding in the Lias, Oolites, and Chalk, but 

 especially characteristic of the Lias. If, however, the Eosaurus 

 Acadiensis (Marsh) of the Coal-measures of Nova Scotia be 

 rightly referred to this order, then the Ichthyopterygia date from 

 the Carboniferous period. Moreover, Prof. Marsh has recently 



