LACEKTILIA. 311 



adaptive kind ; relating in the former to animal food, in the 

 latter to a mixed or vegetable diet. The entire dentition of 

 Echinodon appears so well fitted to pierce the scaly covering of 

 fish, and retain the struggling prey, that I suspect the species 

 to have been ichthyophagous, and, like the Aniblyrhynchus 

 of the Gallopagos Islands,* to have been aquatic in its habits. 



Small vertebrae of true lacertian type have been first found 

 in the Wealden of Sussex. In fig. 103, 4, a is the concave 

 anterior, and b the convex posterior surface of the centrum ; 

 d is the transverse process (diapophysis) ; z is the anterior, and 

 z the posterior, zygapophysis. Such vertebrae are more abun- 

 dant, and have been found associated with other characteristic 

 parts of the species, in the cretaceous strata. On such evi- 

 dence have been based the Rajjhiosaurus subulidens, the Coni- 

 osaurus crassidens, and the Dolichosaurus longicollis* The 

 last-named species is remarkable for the length and slender- 

 ness 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 

 haemal spines, the arches of both of which coalesce with the 

 centrum, and formed the basis of a powerful swimming tail. 

 The teeth are anchylosed to eminences 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 of Mosasaurus has been proposed. 

 Besides the M. Hofmanni of Maestricht, there is a M. Maxi- 



* Owen, "History of British Fossil Reptiles," 4to, pp. 173-183, pis. 2, 8, 9. 



