There are appear to be other ways of spelling John's birth place in 1871 - Mydrim - and suspect this could be him in 1861 living at Mydrim, Carmarthenshire Edit the modern spelling seems to be Meidrim north of St Clears
Theophilus Jones 50 Cobbler b Mydrim, Carmarthenshire,
Mary Jones 62 b Llanwinio, Carmarthenshire
John Jones 20 b Mydrim, Carmarthenshire,
Henry James 8 Boarder
Kay