WEALDEN FORMATIONS. 23 



absence of any surface indicating the overlapping of an adjoining scute, it may be 

 inferred that the bony plates in question studded in an unconnected order the skin of 

 the Hylaeosaur. The diameter of the largest of these scutes does not exceed 3 inches ; 

 the smallest present a diameter of 1 inch. They are flat on the under surface, convex 

 with the summit developed into a tubercle in the smaller specimens, but which is less 

 prominent in the larger ones : the outer surface is studded all over by very small 

 tubercles : the inner surface presents the fine decussating straight lines, which I 

 have described as characterising that surface, in the scutes of the Goniopholis.* 



By the kindness of Dr. Mantell, I was favoured, when preparing my ' Report on 

 Fossil Reptiles,' in 1840, with the means of submitting the structure of a dermal scute 

 of the Hylseosaur to microscopical examination. This structure is represented in T. IX, 

 fig. 1 , and was described in my ' Report ' as follows : 



" The medullary canals, which are stained brown, as if with the hematosine of the 

 old reptile, differ from those of ordinary bone in the paucity or absence of concentric 

 layers. They are situated in the interspaces of straight, opaque, decussated filaments, 

 which frequently seem to be cut short off close to the medullary canals. Very fine 

 lines may be observed to radiate from some of the medullary canals : irregularly shaped, 

 oblong, and angular radiated cells are scattered through most parts of the osseous 

 tissue, but they present less uniformity of size than do the Purkinjian cells in ordinary 

 bone. The most striking characteristics of the dermal bone are the long, straight, 

 spicular fibres which traverse it, and decussate each other in all directions, repre- 

 senting, as it seems, the ossified ligamentous fibres of the original corium."f 



Dermal Spines? T. IX. 



On the left side of the thorax, partly overlying the left scapula and vertebral ribs 

 in the large slab of stone containing the anterior part of the skeleton, now in the 

 British Museum, there are some large elongated, flattened, pointed plates of bone, three 

 of which seem to follow each other in natural succession (T. IV, d, d, d)> The length 

 of the first of these plates is 17 inches, the breadth of the base 5 inches, equal to the 

 antero-posterior diameter of two vertebrae : they decrease somewhat rapidly in length, 

 the second being 14 inches long, and the third 11 inches long; but they slightly 

 increase in breadth. 



These remarkable bones were regarded by Dr. Mantell J as having formed part of a 

 serrated fringe extended along the back of the animal, analogous to that of the Cyclura 



* 'Reports of British Association,' 1841, p. 71. 



t lb., p. 115. 



X ' Geology of the South-east of England,' p. 323 ; ' Wonders of Geology,' vol. i, p. 402. 



