- 



WEALDEN FORMATIONS. 9 



at once brought into the domain of palaeontology by the discovery of the following 

 parts of the skeleton in almost natural juxtaposition : viz., the anterior part of the 

 trunk (T. IV), including ten of the anterior vertebrae in succession (3 — 10 ), supporting 

 a small fragment of the base of the skull ; the two coracoids (ib., 52), the coracoid 

 extremities of both scapulae (ib., 51), detached vertebrae, several ribs {ib., pi) more or 

 less complete, and some remarkable parts of the dermal skeleton, including, appa- 

 rently, enormous vertical plates or spines (ib., d, d), arranged, as is supposed, in the 

 form of a median dorsal ridge or crest of singular dimensions. 



This specimen is now in the British Museum. It was discovered in 1832, in a 

 block of stone, measuring A\ feet by 2| feet, in the Wealden of Tilgate, Sussex.* 



In the fragment of the cranium may be distinguished the pterygoid elements 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 aperture 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, resembled 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 vertebrae are somewhat flattened below 

 so as to present an obscurely quadrate figure ; most of the anterior dorsals (T. VIII, 

 figs. 10 and 11) are more compressed and keel-shaped below; the sacral (T. V) and 

 many of the caudal vertebrae (T. X) are longitudinally sulcated at their under surface. 

 The structure of the atlas and axis cannot be discerned in the British Museum 

 specimen ; the second (conspicuous) cervical vertebra (T. IV, 4)t has its sides sub- 

 compressed, its under surface rather flattened anteriorly, and the slight angular ridges 

 separating it from the concave lateral surfaces are produced anteriorly into two feebly 

 marked tubercles. The parapophyses, or inferior transverse processes, are developed 

 from each side of the anterior part of the body of the vertebra ; they are subcircular, 

 very slightly prominent, about 7 lines in diameter. 



In the fourth (conspicuous) vertebra (T. IV, 6)t a parapophysis is, also, 

 developed from each side of the anterior part of the body, with the costal surface 

 directed obliquely outwards and forwards. There is a small costal surface at the side 

 of the expanded posterior extremity of the same vertebra, against which a part of the 

 head of a rib abuts ; that and three of the succeeding ribs having their heads applied 

 over the interspace of two contiguous vertebrae, as nearly throughout the thoracic 

 region in Mammalia. 



* 'Proceedings of the Geological Society,' December 5th, 1832, vol. i, p. 410. 



f The Arabic numerals indicate the position which I believe the vertebrae to have had in the entire 

 series forming the back-bone of the Hylseosaur. 



2 



