O ver fifty years ago an important paper on ‘The Kelloway Rock of the Yorkshire Coast’ was published by John Leckenby in this Society's Journal. It dealt chiefly, if not entirely, with the development of the stratum in the neighbourhood of Scarborough. From this rock he recorded over thirty species of ammonites, many of which were new. Several of these were not figured, and they may be said to have remained almost unknown to science, except perhaps locally. Even of those figured it has been difficult to determine from the descriptions and illustrations what were their generic affinities—a task not altogether easy, even when the specimens themselves are handled. It is obvious from the ammonite fauna which Leckenby described that the Kelloway Rock of Yorkshire comprises more than the Kellaways Rock of Wiltshire, that it is in part a calcareous equivalent of the Oxford Clay of the southern counties. But, at the same time, this does not state the whole of the facts: for the ammonite fauna of the Yorkshire stratum is not found, so far as many species are concerned, in the Oxford Clay of the southern counties; while certain species of the Kellaways Rock are absent from the Yorkshire deposit. It therefore becomes of interest to see what the ammonites are, and what zonal series they represent. By the kindness of Prof. McKenny Hughes and Mr. Woods of the Sedgwick Museum, Cambridge, all the types of the ammonites described by Leckenby which are in their possession have been sent