OPHIDIA -27!) 



chalk of St. Peter's Mount, near Maastricht, in 1780. The- 

 vertebrae are gently concave in front, and convex behind : 

 there are thirty-four between the head and the base of the 

 tail; a sacrum seems to have been wanting. The caudal 

 vertebrae have long neural and haemal spines, both of which 

 ; i relies coalesce with the centrum, and formed the basis of a 

 powerful swimming tail. The teeth are anchylosed to emi- 

 nences along the alveolar border of the jaw, according to the 

 acrodont type. There is a row of small teeth on each pterygoid 

 bone. For this genus of huge marine lizard the name Mosa- 

 sawrus has been proposed. Besides the M. Hofmanni of 

 Maestriclit, there is a 31. Maximilliani, from the cretaceous 

 beds of North America, and a smaller species, M. gracilis, 

 from the chalk of Sussex.* The Leiodon anceps of the Norfolk 

 chalk was a nearly allied marine Lacertian.t 



Small pleurodont lizards, known at present only by jaws 

 and teeth, with associated pitted scutes, but which may have 

 had procoelian vertebras, have been discovered in Purbeck 

 beds, and have been referred to the genera Scmrillus, Macel- 

 fodus, etc.t Many small terrestrial Lacertians have left their 

 remains in European tertiary formations. 



Order XI. — Ophidia. 



(iSlow-u-orms, Serpents.) 



Chid: — Vertebrae very numerous, procoelian, with a single 

 transverse process on each side ; no sacrum ; no visible 

 limbs. 



The order Ophidia, as it is characterized in the system of 

 Cuvier, requires to be divided into two sections, according to 

 the nature of the food, and the consequent modification of th< j 

 jaws and teeth. Certain species, which subsist oe worms, 



* Op. cif., p. 185, pis. 1, 2, 9. f Op. cifc., p 195, pi. 10. 



t Quart. Journ, Geol. Soc, No. 40 1854, p 120. 



