CHAPTER VI. 



The Eemaining 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 

 Zealand, 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 posteriorly 

 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 reptiles. 

 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 back-bone presents a nearly similar structure, the vertebras, as shown 

 in the figure on p. 6, 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 enclosing the 

 spinal marrow, so that these two portions are always found detached. The bones 



