The evidence of the systematic position of the Wealden fossil Polacanthus has not been very precise. Mr. Hulke in 1881 regarded the dermal armour as closely resembling that of Scelidosaurus ; and the dermal spines were compared with those of Acanthopholis , Stegosaurus , and Omosaurus , with indications of some differences of structure. It is to the Wealden Hylceosaurus that Polacanthus was most closely allied, the resemblance in their dermal spines being very close, and their tibiæ are stated to be remarkably alike. These views were adopted by Prof. Marsh, who in January 1882 placed Polacanthus in the Scelidosauridge, immediately after Hylceosaurus . When the great tuberculate shield which covers the pelvic region in Polacanthus became known in 1887 by the skill of Mr. J. Lingard in fitting it together and of Mr. Richard Hail in removing the matrix, Mr. Hulke described the pelvis, and found the ilia so blended with the dermal bones that their exact form was not made out. The remains of the os pubis are said to be too fragmentary to give the shape of that bone; but it was thought that indications were recognizable of its division into posterior and anterior parts. I was unable to recognize any indication of that bone on the shield, and the lettering on Mr. Hulke's figure only refers to the ischium and acetabulum. Further search fortunately resulted in detecting the missing pubis as an isolated specimen, collected by Mr. Fox with the other remains, east of Barnes Chine, in the Isle of Wight