The year range is established by the printed stationery, with the address in the centre; CD used this type of notepaper from January 1872 until November 1874.
The photograph that CD sent has not been identified, but he sat for Oscar Gustaf Rejlander in April 1871 and probably ordered some of the photographs in August 1871 (Correspondence vol. 19, letter to Elliott & Fry, 23 April [1871]; CD’s Classed account books (Down House MS)). Prior to this, he had been sending out a very poor photograph of himself (see Correspondence vol. 19, letter to Hinrich Nitsche, 25 April [1871]). In Descent 2: 28, CD had drawn on Maynard’s observations on the mud-turtle (Chrysemys picta) of the United States. Both the letter and photograph are pasted into a copy of Descent.