MR. J. W. HULKE ON THE POLACANTHUS FOXII. 
G59 
As no part of the endoskeleton referable to the scapular region and neck was 
discovered, it cannot be ascertained how far forwards the dorsal shield reached, 
neither from the material in its present state can any inference be drawn of the 
presence of ventral armour. The presence of a hsemal series of tail scutes suggests 
that the belly as well as the back may have been mailed. 
The tissue of the scutes is distinctly bony. The vascular canals in the cortex are 
large and very numerous (Plate 70, fig. 4), suggestive of a stout epidermal covering. 
These remains indicate an animal of low stature whose height at the rump probably 
did not exceed 3 feet. Its strongly marked bones and their large joints speak of its 
immense muscular power, whilst the shortness of its limbs and the anchylosis of the 
lumbar vertebrae welding the loins and the sacrum into a long inflexible rod suggest 
an absence of the lithesome and agile movements of a terrestrial carnivore, and give 
probability to its having been a slowly moving vegetable feeder. 
As regards its zoological position, its dinosaurian marks—the inner femoral trochanter, 
the lower end of the tibia, and the forked ribs—are so plain that its reference to this 
Order cannot be doubted. Its place within the Order is also not uncertain. From the 
Iguanodont family, as represented by its two best known genera Hypsilophodon and 
Iguanodon, Polacanthus differs widely in the form and proportions of its limb-bones 
and vertebrae, and by its very highly developed dermal armour, in comparison with 
which the scutes of Hypsilophodon and Iguanodon may without inaccuracy be called 
flimsy. In its stoutly sheathed, crested tail, and its strong body mail Polacanthus 
repeats two striking features of the Liassic Scelidosaurus. The scuted caudal vertebra 
of Polacanthus sketched in Plate 73, fig. 1, presents a resemblance to the figure 
of a corresponding vertebra accompanying Professor P. Owen’s “ Monograph on 
Scelidosaurus,” which must strike the most superficial observer. 
The trunk armour of Scelidosaurus is, however, much less developed than that of Pola¬ 
canthus , the spinecl scutes of the former, so far as these are known from the types 
preserved in the British Museum, are smaller than those of Polacanthus. The resem¬ 
blance of Polacanthus and Scelidosaurus is not restricted to their armour, for massive 
joints are a feature common to both; the differences of shape and proportion of the 
] imb-bones and vertebrae more than suffice, however, to prove their generic distinctness. 
Omosaurus armatus, Owen, of oolitic times, had as large dermal spines as Polacan¬ 
thus, but their shape is very different. The dermal spines of the Jurassic Stegosaurus 
figured by Professor 0. C. Marsh, in ‘American Journal of Science,’ vol. xix., March, 
1880, plate x., are apparently not smaller than those of Polacanthus, but their form 
differs from these ; - the limb-bones of Stegosaurus are also more slender and the femur 
wants the inner trochanter. From the lower chalk Acanthopholis (Huxley), which has 
also a somewhat similar mail, Polacanthus differs in the greater development of this 
protective covering and in its very dissimilar vertebrae. 
It is to the Wealden Ilylceosaurus that Polacanthus appears most closely related. 
4 q 2 
