LACERTILIA.
(Lizards, ifcrnitora, Iguana.) Clw•.—Vertebrx proccelian, with a single transverse process on each side, and with single-headed ribs ; sacral verte brae not exceeding two : two external nostrils; a foramen parietale in most.
Small vertebrae of the lacertian type have been found in the Wealden of Sussex. They are more abundant, and are associated with other characteristic parts of the species, in the cretaceous strata. On such evidence have been based the Raphiosaurus subulidens, the Coniasaurus crassidens, and the Dolichosaurus The last-named species is remark able for the length and slenderness of its trunk and neck, indicative of a tendency to the ophidian form. But the most remarkable and extreme modification of the lacertian type in the cretaceous period is that manifested by the huge species, of which a cranium five feet long was discovered in the upper chalk of St. Peter's Mount, near Maestricht, 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 hxinal spines, both of which arches 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 saurus has been proposed. Besides the M. Hofmanni of Maestricht, there is a M. Maximilliani, from the cretaceous beds of North America, and a smaller species, M. gracilis, from the chalk of 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 proccelian vertebrae, have been discovered in Purbeck beds, and have been referred to the genera Saurillus, Macel lodus, etc..1 Many small terrestrial Lacertians have left their remains in European tertiary formations.