CRETACEOUS FORMATIONS. 25 



the vertebrae situated between the skull and the scapular arch. The number of 

 vertebrae so situated in modern Lacertians is usually five, and rarely exceeds six : in 

 the Bolichosaurus it was seventeen. In modern Lacertians the bodies and neural arches 

 of such cervicals are scarcely inferior in breadth to the succeeding vertebrae, and 

 commonly surpass them in depth by reason of the largely developed inferior spinous 

 processes. The short anterior pleurapophyses are usually thick, broad, and expanded 

 at their extremities, or are " hatchet-shaped" (Cyclodus, Tiliqua, Scincus). Besides the 

 superior number of the cervical vertebrae in the Bolichosaurus, they exhibit a more 

 decided decrease of size as they approach the head : the pleurapophysis of the third or 

 fourth vertebra is short, almost straight, and very slender : that of the eighth or ninth 

 vertebra is also very slender, and but a little longer : those of the three succeeding 

 vertebrae progressively, though slightly, increase in length, but the vertebral ribs 

 do not exhibit their normal length until the seventeenth or eighteenth vertebra : the 

 pleurapophysial character of these eighteen or twenty anterior vertebrae is much 

 more like that of the same vertebrae in the Ophidian than in the existing Lacertian 

 reptiles : and there is no trace of any of the vertebral ribs having supported sternal 

 ribs, or having been attached by these to a sternum. The slender anterior ribs 

 increase in length, however, more gradually in the Bolicliosaurns than in Serpents. 



The occipital region of the fossil skull, with the atlas and dentata, have been too 

 much crushed to allow of their structure being accurately determined and compared : 

 the first tolerably entire vertebra appears to be the fourth from the head : the expanded 

 back part of the neural arch receives the contracted fore part of that arch of the fifth 

 vertebra : the base of the neural spine is slightly expanded posteriorly. In the fifth 

 and succeeding ve'rtebrae, the anterior articular processes look upwards, the posterior 

 ones downwards, and they are simple as in ordinary Lizards, but rather longer and 

 more slender. The thin base of the neural spine extends along the middle of the 

 summit of the entire arch ; the sides of which slope downwards and outwards more 

 gradually, i. e. do not curve outwards so suddenly as in the Iguana and Cyclodus. The 

 short convex diapophysis (d) supporting the rib is developed from the side of the fore 

 part of the centrum beneath and a little behind the anterior zygapophysis. I excavated 

 the chalk beneath the seventh vertebra, and exposed a short compressed 'hypapo- 

 physis/ or inferior spine projecting downwards from the middle of the hinder half of 

 the centrum. The ribs are hollow, as in the Cyclodus* and in Ophidians. The long 

 pleurapophyses of the twentieth and succeeding vertebrae are more compressed than in 

 the Iguana and Cyclodus : they are less regularly or gradually curved ; the comparatively 

 straight middle portion after the first slight bend is too constant in the ribs of the 

 fossil not to be natural : this shape of the ribs indicates the abdomen to have been 



* The vertebral ribs (pleurapophyses) are probably hollow in other Lacertians, but I cite only the 

 genus in which I have found them so in the present comparison. 



4 



