Attention having recently been directed to this subject, I have been induced to present the results of many years' collecting in the Carboniferous Limestone of North Wales. The formation there presents four well-defined subdivisions, each of them, with the exception of the highest, having distinct lithological characters, viz.: Lower Brown Limestone, Middle White Limestone, Upper Grey Limestone, and the Upper Black Limestone. Lists of the fossils have been made, collected more or less continuously along the country from each subdivision.