l haven't come accross a Decimus as yet.
My husbands side of the family originated in Staffordshire 1811. They appear in diferent parts of Staffs, Yorkshire, Manchester, Liverpool and most other places so Decimus could well be a branch.
Variations crop in most names so l wouldn't discount Elizabeth just yet.
Could you tell me what year Decimus and Elizabeth were born so l can try to see if there is a link.