VERTEBRATA : REPTILIA. 545 



London Clay of Sheppey. The nearly-allied Palaophis typhceus 

 of the Eocene beds of Bracklesham appears to have been a 

 Boa - constrictor - like snake of about twenty feet in length. 

 Other species of Palceophis have been described from the Ter- 

 tiary rocks of the United States, and the genus Dinophis has 

 been formed for the reception of another gigantic constricting 

 serpent from the same formation. In some of the later de- 

 posits have been found the poison-fangs of a venomous snake. 

 Upon the whole, however, the Snakes must be looked upon as 

 a comparatively modern group, and not as one of any great 

 geological antiquity. 



CHAPTER LXI. 

 LACERTILIA AND CROCODIL1A. 



ORDER III. LACERTILIA. The third order of Reptiles is that 

 of the Lacertilia, comprising all those animals which are com- 

 monly known as Lizards, together with some serpentiform 

 animals, such as the Blind-worms. The Lacertilia are distin- 

 guished by the following characters : 



As a general rule, there are two pairs of well-developed limbs, 

 but there may be only one pair, or all the limbs may be absent. 

 A scapular arch is always present, whatever the condition of the 

 limbs may be. An exoskeleton, in the form of horny scales like 

 those of the Snakes, is almost always present. The vertebra of 

 the dorsal region are proccelous or concave in front, rarely amphi- 

 cKlous or concave at both ends. There is a single transverse pro- 

 cess at each side, and the heads of the ribs are simple and 

 undivided. There is either no sacrum, or the sacral vertebrae 

 rarely exceed two in number. The teeth are not lodged in dis- 

 tinct sockets (some extinct forms constituting an exception to this 

 statement}. The eyes are generally furnished with movable eye- 

 lids. The heart consists of two auricles and a ventricle, the latter 

 partially divided by an incomplete partition. There is a urinary 

 bladder^ and the aperture of the cloaca is transverse. 



As a general rule, the animals included under this order 

 have four well-developed legs (fig. 301), and would therefore 

 be popularly called " Lizards." In some (Chirotes) there are 

 no hind-feet ; in some (Bipes) the fore-limbs are wanting ; and 

 others (Anguis, Pseudopus, and Amphisbcena) are entirely desti- 

 tute of limbs, thus coming closely to resemble the true Snakes 



2 M 



