At the time of his death, John William Salter (1820–69) was dubbed 'the prince of palaeontologists'. A true naturalist with a particular interest in Trilobita, he started publishing this monograph in 1864, and three further parts were issued in 1865–7. But his heath failed and he died, leaving around half of the trilobites then known from Britain unclassified; the work was wound up in 1883. Though unfinished, Salter's monograph has thirty excellent plates which make it an essential starting point for the study of British Devonian, Silurian and Ordovician trilobites. The monograph is also frequently cited because Salter's 'preliminary classification of trilobites', though brief, was the best devised up to that time, and has since served as a framework for the classifications used today. Salter introduced four orders of trilobites, three of which - Phacopida, Asaphida, Agnostida - are generally recognised today; only his group 'Ampycini' is not now used.