Attention is drawn to the one side remaining of a nineteenth-century correspondence addressed to Alexander Somerville that is housed in the archives of the Scottish Association for Marine Science at Oban, concerning conchological matters. Previously unstudied letters from James Thomas Marshall shed new light on the practicalities of offshore dredging by nineteenth-century naturalists in the Clyde Sea Area; on personalities within conchology; on the controversies that raged among the conchological community about the production of an agreed list of British molluscan species and on the tensions between conchology and malacology. In particular, the criticism of Canon A. E. Norman's ideas regarding taxonomic revision of J. G. Jeffreys's British conchology, as expressed by Marshall, are highlighted.