In 1871 the Geological Department of the British Museum acquired the celebrated collection formed by Professor van Breda at Haarlem. It was especially rich in the remains of fossil reptiles from Maastricht; and among the bones of Mosasaurus were arranged five other specimens, which Mr. William Davies, F.G.S., soon recognized as Dinosaurian. So far as is at present known, these are the most recent evidences of the Dinosaurian order in geological time; and in view of this fact, I am happy in having the permission of Dr. Henry Woodward, F.R.S., the Keeper of the Department, to offer the Geological Society some account of the structure of the last known survivors of the group. I avail myself the more readily of this permission, since I do not remember to have seen in any of the continental museums other specimens exhibited which would add materially to the British-Museum evidence or modify my conclusions.