Thanks Brown1777, yes the townlands are contiguous, and there are certainly cases where boundary change complicated things, and people used older names for townlands but in this case my Robert Allen seems to have been in Glenleary in most or all records and William Allen seems to have been in Camus. While checking them on the Val maps on Askaboutireland i noticed something which i will have to explore more in Deeds or somewhere. In Ballyness on the Bann shore, a Robert Allen, immediate lessor, was listed as possessor of an unoccupied house and offices valued at £14, ie more than the Robert Allen holding in Glenleary. This cannot be my ancestor, but it may be that it was a descendant of the mysterious (to me!) Andrew Allen of Coleraine, linen draper, who was mentioned in a1770 deed re one sixth of the lands of Glenleary. More work required!