Dr. Francis Baron Nopcsa — British Dinosaurs. 249 



Tnentioned. Two such caudal spines measure each 21 cm., two 

 others 19, and so on. Besides this the peculiar features of the 

 two largest, the two next, and so on, is always similar, so that 

 arranging the spines according to the colour and size we get a series 

 attaining the presumed length of the tail oi Polacantlius. This alone 

 would be enough to prove that the plate-like scutes were arranged 

 in pairs along the tail, but besides this and the comparison with 

 Scelidosaurus there is yet another point to prove it. 



By carefully uniting some fragments I managed to bring two 

 plates of equal size still united with matrix in close contact 

 with an underlying vertebra, and this piece, as well as the 

 nnsymmetrical character of two uncrushed pieces (which prove to be 

 the before-mentioned last pair of scutes), shows that the roof-like 

 plates could not have been arranged in any other manner than 



Fig. 7. — Anterior dorsal derraal spine of PolacantJms, interior (median) yiew. 



indicated in the reconstruction. Thus the whole top of the tail of 

 Folacantlius was covered with two rows of diverging, broad, sharp- 

 edged plates, while the button-like ossicles were distributed between 

 them so as to cover the empty spaces. 



In consequence of their great antero-posterior length each of the 

 main scutes was not fixed merely on one but on two or three caudal 

 vertebrEe, thus restricting, together with the ossified tendons, the 

 movement of the powerful tail. 



Having finished with the tail and its armour, the question where 

 to place the dermal spines (Fig. 7) of Polacanthns became quite 

 easy. They could neither belong to the tail nor to the lumbosacral 

 region. They come, therefore, evidently from the anterior part 

 of the body. They are asymmetrical ; according to their size they 

 can be arranged in pairs, and the rows thus formed attain a length 

 -of 150 cm. Kibs and free dorsal vertebree show that the thoracic 



