By the Carboniferous Period, only one order of trilobites, the Proetida, remained. Two superfamilies are represented, the Proetoidea and Aulacopleuroidea. It has been traditionally assumed that only a handful of trilobite genera are present in Carboniferous rocks, but well over sixty are now recognized. Certain facies in the Carboniferous in Britain contain an abundance of trilobites, with maximum diversity being achieved in carbonate mudmounds, as developed, for example, in the Craven area of North Yorkshire, in the Peak District and in north Wales. The only monographic treatment was published 120 years ago, and is now very much out of date, and a new monograph was started in the late 1980s. Work is well on towards its completion. Much of the data gathered will be used in the revised trilobite volume of the Treatise on Invertebrate Paleontology (q.v.)
Once the basic taxonomy has been completed, it is proposed to prepare a phylogenetic analysis, which it is hoped will provide some progress in answering some of the outstanding questions about identification of ancestral groups in the Devonian, and in inter-relationships between the various Carboniferous taxa.