Arthur Earland and D’Arcy Wentworth Thompson corresponded for a period of over fifty years between 1894 and 1946. During this interval Earland supplied Thompson with Foraminifera for his growing museum collection at the University of Dundee. Following Thompson’s move to the University of St Andrews in 1917, a new collection was started. The content, general state, and labelling of the 405 slides in this collection are described. Earland’s correspondence with Thompson provides a rare insight into the early twentieth century approach to scientific research by the interested amateur and sheds new light on the nature of Earland’s long working relationship with Edward Heron-Allen.