Emerson, Ralph Waldo, and Thomas Carlyle.
Correspondence, 1834-72. 2 v. 1883
A reference is required under the editor's name, thus
Norton, Charles E. (Ed.) See Carlyle, Thomas.
Most catalogues will have a goodly number of entries under Carlyle. To enlarge the reference sufficiently to describe the particular book involves a reference as long as an entry. In such case give the entry
Norton, Charles E. (Ed.) Correspondence of
Thomas Carlyle and Ralph W. Emerson. 2 v.
1883
or, shorter still,
Norton, Chas. E. (Ed.) Correspondence of Carlyle
and Emerson. 2 v. 1883
This is better than a reference, as it takes up no more room and saves the searcher the trouble of turning to another part of the catalogue. A book of this kind, obviously, has no subject-entry.
In the classified catalogue a dual book like this needs two entries—one in 816.3 (American Letters) for Emerson, and another in 826.8 (English Letters) for Carlyle, with the index entries
Carlyle, Thos. Correspondence with Emerson, 826.8
Emerson, R. W. Correspondence with Carlyle, 816.3