258 PALAEONTOLOGY 



ceeding two in numbei : body supported on four strong 

 unguiculate limbs. 



The well-ossified vertebrae, large and hollow limb-bones, 

 and tritrochanterian femora of the thecodont reptiles of the 

 Bristol conglomerate, together with the structure of the sacral 

 vertebrae in the allied Belodon, indicate the beginning, at the 

 triassic period, of an order of Reptilia which acquired its full 

 development and typical characteristics in the oolitic period. 



Genus Scelidosatjeus, Ow. — By this name is indicated a 

 Saurian with large and hollow limb-bones, with a femur, 

 having the third inner trochanter, and with metacarpal and 

 phalangial bones, adapted for movement on land. The fossils 

 occur in the lias at Gharmouth, Dorsetshire. 



Genus Megalosaurus, Bkld. — The true dinosaurian cha- 

 racters of this reptile have been established by the discovery 

 of the sacrum, which consists of five vertebra?, interlocked by 

 the alternating position of neural arch and centrum. The 

 articular surfaces of the free vertebrae are nearly flat ; the 

 neural arch develops a platform which in the anterior dorsals 

 supports very long and strong spines. 



The compressed piercing and trenchant form of tooth which 

 characterises the existing varanian lizards was manifested 

 by the Megalosaurus. The specimen which is most illustra- 

 tive of the dental peculiarities of this gigantic reptile is a 

 portion of the lower jaw with a few teeth. The first cha- 

 racter which attracts attention in this fossil is the inequality 

 in the height of the outer and inner alveolar -walls : a similar 

 inequality characterizes the jaws of almost all the existing 

 Lizards. But in these the oblique groove, so bounded, to 

 which tin' l.ases of the developed teeth are anchylosed, is 

 much more shallow, and is relatively wider ; and the teeth in 

 all the stages of growth are completely exposed when the gum 



has been removed. 



