The year is conjectured from the relationship between this letter and the letter to Japetus Steenstrup, 11 September 1876 (Calendar no. 10594), which states that CD received Steenstrup’s photograph a year or two ago.
Steenstrup’s photograph has not been found in the Darwin Archive–CUL. He had provided specimens for CD’s research on fossil and living cirripedes (see Correspondence vols. 4 and 5, and Correspondence vol. 7, Supplement).