ON BRITISH FOSSIL REPTILES. Il7 



to be attained by the choice being present to the mind of subsequent fortu- 

 nate discoverers of these remains of the Hylceosaurus, than if they were solely 

 preoccupied by the hypothesis of the dorsal fringe. For example, it may lead 

 to more careful noting of the constancy or otherwise of the unsymmetrical in- 

 clination of the convex margin of the spine, and whether they form, or are 

 disposed in, pairs ; which, on the costal hypothesis, may be expected, in the 

 event of another skeleton being discovered. 



Bones of the Extremities. 



Scapular arch. — The scapula of the Hylceosaurus* is longer and narrower 

 than in the Monitors and Iguanas, adhering in this respect to the Crocodilian 

 type, but most resembling in the shape of its blade or body, that of the genus 

 Scincus. It differs, however, from the scapulae of all known reptiles, and 

 indicates an approach to the Mammalian type, by the production of a strong 

 obtuse acromial ridge, separated by a deep and wide groove from the hume- 

 ral and coracoid articular surfaces. The blade of the scapula is long, flattened, 

 slightly convex on the inner and proportionally concave on the outer sur- 

 face : the anterior margin is convex, the posterior one concave ; the upper 

 extremity or base truncate, slightly convex, with the posterior angle a little 

 produced, the anterior angle rounded off. On the outer side of the scapula 

 two broad convex ridges descend and converge to form the beginning of a 

 thick and strong spine, at fourteen inches distance from the base ; this then 

 expands into the thick acromial ridge, which extends transversely, and is con- 

 tinued forwards as a long subprismatic process from the anterior angle of 

 the head of the scapula. This process, which appears likewise to be present 

 in the scapula of the Iguanodon, perhaps also in the Megalosaurus, is broken 

 off in the present specimen about four inches from the neck of the scapula, 

 with which it forms a right angle. The acromion is perforated at the base of 

 its anterior prolongation by a foramen analogous to the supraspinal one in the 

 scapula of the Edentate Mammalia. Besides the scapulae preserved in the 

 connected part of the skeleton, there is, in the Manteliiau Museum, a nearly 

 entire and detached scapula of larger size, discovered, in connexion with many 

 other bones of the skeleton, in a layer of blue clay near Bolney in Sussex, 

 and indicating the connected part of the skeleton first discovered in 1832 to 

 have belonged to an immature individual. The dimensions of this scapula 

 ai"e as follows : — In. Lines. 



Length of the scapula 18 



Breadth of its base 8 



Breadth of its neck 3 9 



Thickness of its base 1 



Thickness of its neck 2 6 



Breadth of subacromial groove 2 



Breadth of humeral articulation 4 



Breadth of coracoid articulation 2 6 



The coracoids present a much more simple form than in the Megalosaurus, 

 and resemble those of the Scink and Chameleon, thus deviating in their great 

 breadth, like the coracoids of the Enaliosaurs, from the Crocodilian type. In 

 the portion of the skeleton the right coracoid is slightly bent out of place and 

 thrust under the left one ; and there is no trace of a sternal or entosternal bone 

 in their interspace. The median margin of the coracoid describes an unin- 



* I have been favoured by Dr. Mantell vrith a drawing of the scapula figured by him in his 

 recent Meuioii- on ihe Hylceosaurus, Phil. Trans., 18tl, pi. x. fig. 10. The description above 

 given of this, as of all the other Tilgate Saurians in the present Report, is taken from the 

 original specimens in the British Museum, and other depositories of the Wealden fossils. 



