(A) Introduction A list of the species of ammonites, identified by me, has already been included in Dr. Lang's stratigraphical account. It is intended here to review and amplify these identifications, and to attempt to justify the generic classification which I have adopted, also to discuss the phylogenetic relations of some of the ammonites of the Lower Lias. The development of a number of important types here dealt with, for instance, Arnioceras, Agassiceras, Arietites, Cymbites, Xipheroceras, Microderoceras, etc., was studied some years ago; but only brief reference can be made to this ontogenetic work, and it is also impossible at present to figure the new forms here recorded. It is a matter for regret that, in the absence of detailed stratigraphical work and careful zonal collecting for other districts, exact correlation is as yet impossible; and, for this reason, but little help was obtained from a study of the splendid collections in the British Museum (Natural History), of the genus Arnioceras, from Yorkshire and the Midlands, for instance. On the other hand, my Arnioceras material from Skye, described separately, proved of use, and confirmed what, so long ago as Dumortier's time, was surmised of the enormous range of this genus, although sufficient emphasis had not been laid upon it in previous accounts of the Dorset succession. Also, a collection made by the late Sir Henry Butlin, and recently presented to the British Museum (Natural History), contains a number of ammonites from Stockton in Warwickshire; and, since some of them were