The authorship of the anonymous Conchology, or natural history of shells has often been disputed, as has also the correct dating of the parts of this incomplete book. Some have attributed this work — the first in which the term "conchology" was employed — to the wellknown natural history dealer George Humphrey (? 1745—1825), who indeed seems to have claimed authorship in his Museum Humfredianum of 1779. Others have favoured Emanuel Mendes da Costa (1717—91), author of books on shells as well as fossils and minerals. Others again have settled for joint authorship. However, in the absence of detailed biographical data on either of these two men, the question of authorship of the Conchology has been largely a matter of speculation. The key to the puzzle lies in the rather unusual circumstances that attended the production of the book, for it was during this period that da Costa fell from grace, being convicted of embezzlement and spending some years in prison. No-one has hitherto documented this aspect of da Costa's life, while the most valuable source of all, the eleven volumes of da Costa correspondence in the British Library, has been almost entirely neglected. In the light of these letters, a number of which date from the prison period, together with clues in other letters, it is now possible to date the six parts of the book fairly accurately, and also to assess Humphrey's role in it and to conclude that the real author was da Costa, an unrepentent debtor in the King's Bench Prison. Da Costa's downfall, which can be followed closely in the minutes of the Council of the Royal Society for 1767—68, provides the reason why the Conchology was anonymous, and in turn this serves to narrow down the dates within which it was written. Anonymity was essential, for no collector would allow precious specimens to be borrowed for illustration in the name of a man who had embezzled the funds of the Royal Society to the tune of nearly fifteen hundred pounds (by pocketing subscriptions). Various guesses have been made concerning the duration of da Costa's term in prison, but in fact he was committed to the King's Bench Prison in November 1768 and was not released until four years later, in October 1772. During this time he made translations, worked on catalogues and delivered lectures. The letters written and received in prison show that the Conchology was well under way by early in 1771, although it was probably planned at least a year before and may perhaps have stemmed from a more ambitious project covering several animal groups, dating from late in 1767. The true authorship of the Conchology can be deduced partly from the prison letters and partly from a letter written years later to John Swainson, in which Humphrey criticizes da Costa's text for several of the figures. Humphrey's role seems to have been that of editor. The book was illustrated by John Wicksteed (pls. 1–4,), George Humphrey's brother William (pls. 5, 7) and Peter Brown (pls. 8–12), but the text breaks off in the middle of pl. 5. There were six parts, each with two plates, and from the letters and from two dated wrappers with a copy in the British Museum (Natural History), the parts appear to have been issued at two month intervals between December 1770 and October 1771. The abrupt cessation of the work cannot yet be accounted for. The Conchology is not without taxonomic value, some of the plates illustrating type specimens. However, the history of its production throws important light on da Costa, who was a highly significant — if wayward — figure in eighteenth century natural history, and a man who well deserves a more extensive and detailed biography. Subsequently to the Easter Meeting this study has been reported in the following publication: Whitehead, P. J. P. 1977. Emanuel Mendes da Costa (1717–91) and the Conchology, or natural history of shells. Bull. Br. Mus. nat. Hist. (hist. Ser.), 6 (1): 1–24.
The diary of Sir Charles Blagden