Bill, Do you know when and where they married? It is possible Mary was married before. Just looking at their ages and the ages of the children. The birth certificates would have her maiden name, the marriage would have her current married name with father's name (that should be her maiden name or born name). Luckily Francis has a less usual occupation of butcher and father possibly Matthew. In the 1851 census HO107/2397 folio 97 page 5 Francis has a lodger there--Thomas Nell. There is a marriage in St. John the Baptist in 1846 of a Francis Lambert and Mary Nell with the other name Tatter. There is a marriage of Thomas Nell and Mary Tatten in Sunderland 28 Oct 1826. There is a burial of Thomas Nell in 1831 Sunderland. So your mystery name most likely is either Tatten or Tatter. The 1841 census has Mary Nell with most likely her mother Sarah Tatten HO107/321/2 folio 7 page 10, children Thomas Nell and Elizabeth Nell are their also. Janis