Found with more modern envelope inscribed ‘Writers’.
The folder contains the following six letters written by Emile Souvestre variously to Louise Swanton Belloc and her husband Jean Hilaire Belloc (no year given but possibly 1830s?).
Also contains:
Letter from Almira Lincoln Phelps to L S B, 25 November 1880, addressed from Baltimore;
Letter to L S B, April 1881 (?), from Pan...? [signature unclear];
Partial bibliography of Emile Augier [French dramatist 1820-89] with related notes;
Small print of a portrait of ‘H.M. Marie Amélie, Queen of the French, from a portrait by Dalton, after Sir W Ross [no date];
Letter from Louis Boulanger [1806-67, French Romantic painter, lithographer and illustrator] to ‘Mon cher Belloc’ [presumably Jean Hilaire Belloc], addressed from Chateau du Couloumé, 3 November [no year].