This is the third part of a monographic treatment of the latest Caradocian–Ashgillian brachiopods of the Girvan District. Harper is one of the leading students of Ordovician brachiopods, together with Leonid Popov (Cardiff), L. R. M. Cocks (London), Rong Jiayu and Zhan Ren-bin (Nanjing), and Luis Benedetto (Cordoba, Argentina). This treatment describes 25 rhynchonelliformean genera, including one new genus, six new species and two new subspecies. The beautiful illustrations make it much easier to deal with the morphological characteristics of the Girvan Late Ordovician brachiopods. The taxonomy is carefully tied into the local stratigraphic succession, with due attention paid both to the changes in stratigraphic nomenclature used in the Girvan District over time, and also to the local, Girvan distribution, with localities tied into a geological map indicating the local structural situation. Attention has also been given to the biogeographic character of these Late Ordovician shells, with their overall more offshore Laurentian character.

Sample size is provided for all taxa. Careful consideration has been given to the many earlier works dealing with Girvan Late Ordovician brachiopods; prior taxonomic assignments are given for the varied taxa. Up-to-date references are provided for each taxon, and a complete taxonomic index of the brachiopods dealt with in all three parts of the monograph is provided, together with current age assignments.