134 ANIMAL LIFE 'PAST AND PRESENT. 



specimen shown in Fig. 40, and were simpler and rela- 

 tively smaller than those of the Iguanodon, although 

 constructed on the same fundamental plan. This 

 diminution in the size of the teeth, 

 we may observe in passing, appears to 

 be an instance of that tendency to a 

 reduction or disappearance of the teeth 

 in the specialised forms of many groups 

 of animals to which we have alluded in 

 the chapter on tortoises and turtles. 

 YIU. 4o.-side view The Armoured Dinosaurs were also 

 of the tooth of Ar- we ^ ^presented in the Wealden (where 



moured Dinosaur. x 



Enlarged. (After they were first discovered by Dr. Man- 

 tell), although we have at present no 

 evidence as to the nature of their skulls. One of 

 these Wealden reptiles, which has been named the 

 Hyla3osaur (from the Greek liuU, " wood," in allusion to 

 the Wealden, or wooded country), carried a formidable 

 row of large flattened spines forming a crest down 

 the back. The other, termed Polacanthus (many- 

 spined), is remarkable for having had the whole region 

 of the loins and haunches protected by a continuous 

 sheet of bony plate-armour, rising into knobs and spines, 

 after the fashion of the carapace of the Glyptodonts.* 



The earliest evidence of the existence of the Horned 

 Dinosaurs occurs in the greensand of Austria, but the 

 specimens hitherto obtained from these deposits are 

 too imperfect to give us any definite insight into the 

 organisation of these reptiles. We accordingly turn 



* See Chapter I. 



