Sorry, my previous post now looks wrong(!) as I think I have found Elizabeth Jones, husband Hugh Jones and children William, Catherine and Hugh in the 1871 census - living in Chapel Street, Llanddeiniolen, Caernarvonshire (RG10, 5717, 18,9).
Hugh Jones, labourer, 29, b. Llanfaethlu, Anglesey
Elizabeth Jones, wife, 29, b. Menai Bridge
William Jones, son, 8, b. Menai Bridge
Catherine Jones, dau. 4, b Carnarvon
Hugh Jones, son, 5 mo., b. Menai Bridge
Hugh's birth registration has b. 20 Nov 1870 Llandysilio, the son of Hugh Jones and Elizabeth Jones.
Curious that Henry was baptised 1864 as the illegitimate son of Elizabeth Jones.