During the last few months the preparation of a descriptive catalogue of the magnificent collection of reptilian remains obtained by Mr. A. N. Leeds in the Oxford Clay of Peterborough, has rendered it necessary to examine in some detail the fine series of more or less complete skeletons of Ophlhalmosurus preserved in the British Museum. In the course of this examination a certain number of new facts have come to light, and since it will be some time before the detailed description can appear it seems desirable to give a brief account of some of the more interesting points.