PURBECK FORMATION. 39 



young Iguanodon, the primary ridge is median and well-marked, and in the 

 unworn tooth forms, or terminates at, the apex of the crown, increasing its resem- 

 blance to the Echinodont type of tooth. The difference of dental structure 

 between Echinodon and Iguanodon is of the 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 fishes, and retain 

 the struggling prey, that I suspected the species to have been ichthyophagous, 

 and, like the Amhlyrhynchus of the Gallopagos Islands,* to have been aquatic in 

 its habits. 



My fellow-labourer in palaeontology, Dr. Falconer, F.R.S., by whose labours 

 that science has been so much enriched, suggested the name Sauraechinodon for 

 the present Purbeck reptile ; but as I am not aware that the more abridged form 

 has been preoccupied, I have adopted Echinodon as sufRciently distinctive, 

 having reference to the almost spiny character of the larger basal serrations of 

 the apical half of the tooth. 



The present species is dedicated to its discoverer, Mr. Beckles, of whose 

 collection of Purbeck fossils the specimens here described form part; and I 

 record with pleasure my grateful sense of the liberality with which they have 

 been confided to me for elucidation. 



* Darwin, 'Voyage of llie Beagle,' vol. iii, p. 4G6. 



