This section provides additional references for each species. Where appropriate, a reference to the distribution map in the 1962 Atlas (Perring & Walters, 1962) or its Critical Supplement (Perring & Sell, 1968), cited as 'Atlas' or 'Atlas Supp.' respectively. For each book the citation is followed by the page number and a letter to indicate the position on the page. For the 1962 Atlas 'a' is used for the map on the top left, 'b' top right, 'c' bottom and 'd' bottom right. The format of the Critical Supplement is less regular, but the maps are numbered in the same sequence.
After this entry, key references are provided for the wider literature on the taxonomy, ecology or distribution of the species.