on british fossil reptiles. ill 



Hyi-^osaurus. 



A second well-marked genus of Dinosaurian Reptiles is founded upon a 

 large portion of the skeleton of the reptile to which the name at the head of 

 this section has been applied by its discoverer, Dr. Mantell. 



In assigning to this genus its present place in the Dinosaurian order, I 

 have been guided by the structure of the vertebral column, especially the 

 sacrum, and by the following considerations. The distinct alveoli in the jaws 

 of the Megalosaurus, and the resemblance of its teeth to those of two ex- 

 tinct Crocodilians, viz. the Argenton species and the Suchosaurus, seemed 

 to claim for that great carnivorous Dinosaur the next place to the Crocodi- 

 lian order, among which the Streptospondyliis, as has been shown, seemed to 

 make the closest approximation to the Megalosaurus, in the great height, 

 complexity and strength of the neural arch of the vertebrae. In the present 

 genus, which there is good reason for believing to have resembled the Lizards 

 more than the Crocodiles in its dental characters, an affinity to the Loricate 

 Sauria is manifested not only by the structure of the vertebrae and ribs com- 

 mon to it with other Dinosaurs, but likewise by the presence of dermal bones, 

 or scutes, with which the external surface was studded. 



The Hylaosaurus has not been made known like the Megalosaurus, from 

 detached parts of the skeleton successively discovered and analogically re- 

 composed, but was at once brought into the domain of Palaeontology by the 

 discovery of the following parts of the skeleton in almost natural juxtaposi- 

 tion : viz. the anterior part of the trunk, including ten of the anterior ver- 

 tebrae in succession, supporting a small fragment of the base of the skull ; 

 the two coracoids, the coracoid extremities of both scapulae, detached verte- 

 brae, several ribs more or less complete, and some remarkable parts of the 

 dermal skeleton, including, apparently, enormous vertical plates or spines, ar- 

 ranged, as is supposed, in the form of a median dorsal ridge or crest of sin- 

 gular dimensions. 



In the fragment of the cranium may be distinguished the pterygoid ele- 

 ments of the sphenoid bone, the inner margins of which touch anteriorly and 

 then recede as they pass backwards, leaving a heart-shaped posterior nasal 

 aperture, the apex of which is turned forwards. The breadth of this aper- 

 ture is 1 inch 3 lines : its posterior position gives another character, by which 

 the present Dinosaur, and probably the larger genera of the same order, re- 

 sembled the Crocodiles more than the Lizards. 



The bodies of the vertebrae are shorter in proportion to their breadth than 

 in the Megalosaurus or Iguanodon. They have not so smooth and polished 

 a surface as in the Megalosaurus, nor are they so contracted in the middle, 

 or so regularly rounded below from side to side ; a few of the anterior ver- 

 tebrae are somewhat flattened below, so as to present an obscurely quadrate 

 figure ; most of the anterior dorsals are more compressed and keel-shaped 

 below : the sacral and caudal vertebrae are longitudinally sulcated at their 

 under surface. 



The structure of the atlas and axis cannot be discerned in the Mantellian 

 specimen ; the second (conspicuous) cervical vertebra has its sides subcom- 

 pressed, its under surface flattened, and the anterior part of the slight angular 

 ridges separating it from the concave lateral surfaces, are produced anteriorly 

 into two feebly-marked tubercles. The inferior transverse processes are deve- 

 loped from each side of the anterior jjart of the body of the vertebra ; they 

 are subcircular, very slightly prominent, about 7 lines in diameter. 



In the fourth (conspicuous) vertebra, a large proportion, but not the whole, 

 of a costigerous transverse process is developed from each side of the anterior 



