Introductory. The following communication treats of certain remains referred to four species of English Mesozoic Reptiles, some of which were first described or named by Professor H. G. Seeley, and also includes a discussion as to the affinities of a fifth form. The substance of that portion of the paper relating to Peloneustes philarchus was previously brought under the notice of the Society at the Meeting held on May 23rd as a separate communication, entitled “On the Skeleton of a Sauropterygian from the Oxford Clay near Bedford”, but, on account of a change of view on the part of the Author, it was considered advisable that it should be again presented in a revised form. Vertebræ of an Ornithopodous Dinosaur from the Canbridge Greensand. On page 621 of a memoir on the remains of Dinosaurs from the Cambridge Greensand, published in the 35th volume of the Society's 'Journal,' professor Seeley applied the name Syngonosaurus macrocercus to a series of nineteen vertebræ from the cervical, dorsal, sacral, and caudal regions, which were said to be associated, and indicate a medium-sized species. At the conclusion of the description of these vertebræ mentions is also made of csrtain dermal scutes. which it was suggested might also be associated. I have no intention of entering into the question whether the alleged association of all these remains is absolutely certain, and I shall accordingly confine my remarks to the one cervical and eight dorsal vertebræ, which, as being the first described (although not figured), may,