Perhaps Mark Synnott is deceased by now? (you didn't mention the date book was published)
Mark Seton Synnot, Esq., Ballynoga, Newtownhamilton mentioned here in 1875:
http://freepages.genealogy.rootsweb.ancestry.com/~econnolly/twextracts/tw18751100.htmlSYNNOT, MARK SETON, of Ballymoyer, Newtown-Hamilton, Co. Armagh.
b. 1820, s. 1874, m. 1843. Armagh
www.rootschat.com/links/06kp"Copy of the Settlement made on the marriage of Captain Corbet Smith of Bitteswell Hall, Leics., a Captain in the 1st Regiment of Dragoons, with Eva Charlotte Synnot, daughter of Mark Seton Synnot the elder of Ballymoyer, Armagh, Ireland. From the profits of the sale of the Manor of Lilburne, Northants., and certain premises and lands in Lilbourne and Walcote, Leics., various sums of money are to be settled on Corbet and Eva and their children. (In 1911 their daughter Ada Emily Corbet married Henry Allesley Ward-Boughton-Leigh.) CR162/541 20th Jan. 1875"
www.rootschat.com/links/06kq1891- The Will of Mark Seton Synnot late of Ballymoyer County Armagh Esquire who died 2 December 1890 at same place was proved at Armagh by Anne Jane Synnot of Ballymoyer the Widow one of the Executors. Effects £8692 2s.
1901- Letters of Administration (with the Will) of the unadministered estate of Mark Seton Synnot late of Ballymoyer County Armagh Esquire who died 2 December 1890 were granted at Armagh to Cecilia Agnes Synnot and Ada Maria Synnot Spinsters. (Former Grant 10 January 1891). Effects £103
See
www.proni.gov.uk