Manuscript oratorios, operas, orchestral pieces, choruses, melodies and other musical compositions (including the four Welsh Airs arranged for choir and full orchestra premiered at the Crystal Palace, 1896); an autographed notebook containing solfa versions of Welsh melodies arranged for male voices, 1915; correspondence, 1934-1935, relating to the proposed publication of a memorial volume to Jenkins by nine of his contemporaries ('Er Cof am yr Athro David Jenkins Gan Naw o'i Gyfoedion'); music exercise books, 1877-1881, and a volume containing blacksmith's accounts, Trecastell, and particulars of payments to preachers, 1796-1810.

Papers of John Morgan Howell of Aberaeron, 1871-1960, including exercise books containing a memorandum for 1871 and a history, in Welsh, of Dr Thomas Phillips, Neuaddlwyd, by J. M. Howell; books of press cuttings containing articles relating to Aberaeron, 1873-1931, operas, 1920-1960 (collected by G[eraint] M. Howell), and the poetry, 1889-1921, of Margaret Aeron Davies; and articles by J. M. Howell, 1897; family correspondence, 1888-1926, and miscellaneous letters and papers, 1875-1946; a volume of typescript copies of Christmas carols in Welsh composed by J. M. Howell, collected and bound by J. Seymour Rees, 1941; and a pedigree of the Howells family of Penybaily, parish of Llangunllo; together with some papers of his daughter, the late Mrs Nesta Poulgrain (née Nesta Howell), including a diary of a journey to Naples [by Mrs Poulgrain, 1937]; and exercise books, containing a copy of the diary and poetry (1918).