ON BRITISH FOSSIL REPTILES. 119 



racteristic of the more gigantic Wealden reptile. The main calcigerous tubes 

 are characterized by the slight degree of their primary inflections ; they are 

 continued in an unusually direct course from the pulp-cavity to the outer sur- 

 face of the dentine, at nearly right angles with that surface, but slightly in- 

 clined towards the expanded summit of the tooth. They are chiefly remarka- 

 ble for the large relative size of their secondary branches, which diverge from 

 the trunks in irregular and broken curves, the concavity being always to- 

 wards the pulp-cavity. In most parts of the tooth, the number of these 

 branches obscures even the thinnest sections. 



The ossified pulp exhibits the parallel concentric layers of the ossified mat- 

 ter surrounding slender medullary canals, and interspersed with irregular el- 

 liptical radiated cells. 



Jaw of the Hylceosaurus? — No.g^^^s' i" *^^^ Mantellian Collection, is a por- 

 tion of the right ramus of the lower jaw, with characters distinguishing it from 

 that of any other known Saurian; as, for example, its degree of curvature, in- 

 dicating the lower jaw to have been bent down in an unusual degree, and the 

 remarkable inequality of its external surface. This fragment is about three 

 inches long, one inch seven lines deep at the hind part, and one inch five lines 

 deep at the fore-part ; flattened and smooth at the inner side, but having the 

 outer side raised by the termination of a strong angular ridge at its lower and 

 hinder part, and by a rough convex longitudinal ridge extending along its 

 upper part ; the surface of the jaw being concave above and below this ridge. 

 The lower margin is thick and convex ; the upper one is formed by a regular 

 series of pretty close-set sockets, with the internal alveolar wall broken away, 

 displaying their partitions ; but with the outer wall entire, thin and slightly 

 crenate at its upper margin. 



At the hind part of tliis fragment the anterior extremity of the opercular 

 piece is preserved ; the rest is formed exclusively by the dentary piece : the 

 area of the wide conical cavity in the interior of the jaw is exposed at the 

 back part of the fragment ; its apical termination is near the fore part. A 

 succession of large vascular canals open obliquely forwards in the concavity 

 above the upper oblique longitudinal ridge. The whole of the outer surface 

 is minutely ridged and punctate. 



The depth of the sockets bears a smaller proportion to that of the jaw than 

 in modern Lacertians or Crocodiles, being about one-fourth of that depth : 

 the partitions of the sockets, which are very regular in their breadth and 

 depth, though they are more prominent than in the pleurodont Lizards, yet 

 exhibit a fractured margin ; there is no trace of a smooth natural surface of 

 the bone in the interspace of the sockets; and at the part where the inner 

 wall has been least mutilated, it nearly completes the socket and incloses the 

 long and slender fang of the tooth. Whence, I conclude, that the entire jaw 

 of the extinct reptile would have exhibited a series of true sockets, not de- 

 pressions merely, as in the pi'esent mutilated fragment, and that it would 

 have agreed with the Megalosaurus in presenting the thecodont mode of at- 

 tachment of the teeth. 



The crowns of all the teeth are broken off"; the small sockets of reserve, 

 exposed at the inner side of the base of the old sockets, do not contain any 

 evidence of the species to which this fossil has belonged. In the absence of 

 this characteristic part of the tooth, an element in guiding our choice between 

 the Iguanodon and HylcEosuurus is given by the breadth of the interspaces 

 of tiie sockets ; these must bear relation to the breadth of the crowns of the 

 teeth, if we suppose that they were in contact throughout the series, as in 

 Lacertians. Now the teeth of the Iguanodon, and those which I have re- 

 ferred to the HylcEosaurus, diff"er in a marked degree in the breadth of the 



