Fortescue William Millett (1833‒1915) was one of the leading micropaleontologists of the late nineteenth century. His work concentrated on modern and living foraminifera, some of which were collected from the marine sediments around Cornwall and Devon. He also studied the marine clays of the St Erth Formation, which contain a distinctive and diverse assemblage of foraminifera and ostracods together with some enigmatic, spiny microfossils. The presence of these Pliocene sands and clays, perched on the Paleozoic basement, provides evidence of sea levels significantly higher than the present day. Following Millett’s death in 1915, Edward Heron-Allen purchased his samples, slides and notes, placing them in the collections of the Natural History Museum in London where they remain available for study. The diversity of the microfossil assemblages has been further investigated since the 1970s, and remains of significant interest.