Previous palaeoecological researches have in large measure arisen as subsidiaries of stratigraphical and palaeontological studies. The conclusions drawn have necessarily been confined to broad generalizations on the depositional environments, or to elucidation of the modes of life and the habitats of related groups of fossils- So far as had been ascertained at the commencement of this research, there had been no detailed palaeoecological study of a fossil assemblage from a limited marine horizon. Such a study seemed necessary and the research described in this thesis is an endeavour to contribute towards the knowledge and understanding of fossil benthonic communities. The objects of the research were twofold to discover how the various fossils of a particular marine deposit had lived, and to reconstruct the physical and biological environments prevailing during the accumulation of that deposit. The study has been confined to a detailed analysis of the fossil assemblage from a shale, two feet in thickness, of Lower Carboniferous age. The objects of the research have for the most part been achieved, and, in particular, the results have shown that larval studies may be of greater importance in palaeontology than has hitherto been realised. The problems encountered have necessitated an approach based on recent ecological studies of living animal communities.