This says it's a bridge over the canal at the North Circular Road. The existing canal doesn't cross NCR, however. Maybe, it's the filled in bridge at Phibsboro that crosses the old spur, leading into Blessington Basin.
E. Over the Royal Canal (proceeding from the Liffey):-
1. Newcomen-br. (North-strand.)
From Sir Wm. G. Newcomen, bart. (cr. 1781), a director of the Royal Canal Company in 1791.
2. Clarke's-br. (Ballybough-rd.)
From Edw. Clarke, a director in 1791.
3. Clonliff-br. (Jones's-rd.)
From the adjoining townland of Clonliff.
4. Binns-br. (Drumcondra-rd.)
From John Binns, a director in 1791.
5. Blaquiere-br. (N. C. R.)
From the Rt. Hon. Sir John Blaquiere, bart, a director in 1791.
6. Westmoreland-br. (Glasnevin-id.)
From the Earl of Westrnoreland,~L.L. 1790-95.
From Henry Stevens Reilly, a director in 1791.