from the Louver Chalk. 14* 



cellular. The outline of the posterior end of the vertebra is 

 pentangular, as high as wide. The height of the ball appears 

 to be less than the depth of the cup. 



Of the vertebral differences of Serpents and Lizards little is 

 known. This fossil resembles a serpent more than could have 

 been expected, and yet in other modifications comes near to the 

 Lizards. A Cretaceous serpent may have been more Lacertian 

 than any now known, and a lizard of the Chalk may have been 

 more Ophidian. 



The chief Lacertian features which I detect are — 



(1.) The absence of an hypapophysis, which all serpents ap- 

 pear to have, though in some (as in Python) it is very slight. 



(2.) The depressed centrum, with transversely oval and over- 

 hanging cup and oblique ball, are Lizard characters, though the 

 cup is oblique in Crotalus, Paleryx depressuSy &c., and the ball 

 is transversely elliptical in some other forms. 



(3.) The absence of additional diapophyses besides the costal 

 tubercle is characteristic, though they are not found in all 

 Ophidia. 



(4.) The neural arch is not notched between the zygantra, as 

 in Serpents, but is prolonged back a little between and over 

 them, as in Iguana. The zygantra are excavated in the middle 

 of the sides of the neural canal, as in Iguana, and not at its 

 summit, as in most serpents, though Naja, Hydras, Natrix, &c., 

 are exceptions. 



(5.) The zygosphene projects well over the cup, as in. Iguana, 

 and is not level with it, as in Ophidians. 



(6.) Iguana has similar basal ridges, and depressions under 

 the costal tubercle, like those in the fossil, only more developed. 

 But neither in lizards nor in serpents does the basal ridge meet 

 the ridge between the zygapophyses, because the costal tubercle 

 is always lower down. 



The more marked Ophidian characters are — 



(1.) The broad quadrate form, which is nearer to Palaophis 

 than to Iguana, though the. anterior vertebrae of this and most 

 lizards are as short. In Scincus there is much the same general 

 form of the vertebra, and a like absence of neural spine and 

 hypapophyses ; but the zygosphene can hardly be said to exist, 

 the zygapophyses are never horizontal, and are well raised above 

 the tubercle for the ribs. 



(2.) The horizontal zygapophyses, level with the top of the 

 cup, find their parallel in Eryx and most Serpents; but in 

 Iguana, the nearest to it of the Lizards, they are higher. Iguana 

 wants the sharp ridge connecting the zygapophyses ; it is cha- 

 racteristic of some serpents, but is also found in Scincus. 



The balance of evidence from the few data at my command 



11* 



