CHAPTER VI 



THE REMAINING GROUPS OF REPTILES ORDERS ICHTHYOPTERYGIA, 

 RHYNCHOCEPHALIA, AND ANOMODONTIA 



OF THE three orders remaining for consideration, two are completely extinct, 

 and not known from deposits of later date than those of the Secondary period, while 

 the third is represented at the present day only by a single species from New Zea- 

 land, although in former geological epochs it appears to have been abundant. The 

 first of the three for consideration is the group of 



FISH LIZARDS Order ICHTHYOPTERYGIA 



More or less familiar to all from the beautifully preserved skeletons obtained 

 from the Lias of England and the Continent-, specimens of which are exhibited in 

 almost every museum, the Fish Lizards, or Ichthyosaurs, were large marine reptiles, 

 with the naked body thick and whale-like, the neck extremely short, and the limbs 

 modified into paddles differing from those of all other members of the class in the 

 structure of their skeleton. The skull is produced into a long snout, generally 

 furnished with a full series of sharp teeth, and mainly formed in the upper jaw by 

 the premaxillary, or front jawbones; and the nostrils are consequently placed close 

 to the eyes, the latter, like those of birds, being provided with a ring of movable 

 plates. Superiorly, the skull has a hole or foramen in the parietal bones; while pos- 

 teriorly the upper and lower arches are connected behind the socket of the eye by a 

 bone known as the supratemporal, so that this portion of the skull is completely 

 roofed over, as we shall see to be the case in the Labyrinthodont Amphibians. 

 Then, again, the quadrate bone, with which the lower jaw articulates, is firmly 

 united to the adjacent elements of the skull; while in the general relations of this 

 bone and the bones of the palate there is a marked agreement with the beaked rep- 

 tiles. The teeth are confined to the edges of the jaws, where they are implanted in 

 distinct sockets, and generally have conical and fluted crowns, although more 

 rarely they are compressed and smooth, with sharp cutting edges at the front and 

 back. The backbone presents a nearly similar structure, the vertebrae, as shown 

 in the figure on p. 2362, being short discs, which may be either deeply cupped or 

 nearly flat at the two ends. In the body and neck these vertebras carry a pair of 

 tubercles on each side for the articulation of the forked ends of the ribs; but in the 

 tail there is but one such tubercle, the ribs being single headed. Moreover, the 

 vertebras are further remarkable for the absence of any body union between 

 the body or centrum (the part represented in the figure) and the arch inclosing the 

 (2614) 



