These two short monographs, published under the auspices of the Palaeontographical Society in 1851 and 1854, show Charles Darwin as a meticulous research scientist, poring over fossils collected by himself and other enthusiasts in Britain and in Europe. The first volume is devoted to the Lepadidae, and the second to the Balanidae and Verrucidae (all types of barnacle, members of the infraclass Cirripedia). Darwin's interest in barnacles had first arisen in his student days in Edinburgh, under the guidance of Robert Grant, and increased during his detailed work in dissecting and classifying the specimens he had collected on the Beagle voyage. The publication of his findings cemented his reputation as a expert taxonomist and biologist, and his observations over eight years of the minute differences between males, females and an apparent hermaphroditic stage of development lent support to his developing theory of evolution.