The frequent distinction made between scientific and purely amateur collections misrepresents the specificity of the field of eighteenth-century natural history. This paper argues that the extent and the boundaries of a scientific field can be determined only within the framework of concrete historical constellations of institutions, protagonists, practices and objects. By tracing the circulation of shells in eighteenth-century France, Paris in particular, between about 1735 and 1780, it becomes evident which individuals or groups actually came into contact with these shells; in what practices of collecting, describing and classification they were involved; and in what spaces they were displayed. Thus the contours of a constellation emerge which differ considerably from those drawn hitherto.