An unusual gold and enamel mourning ring

An unusual gold and enamel mourning ring, decorated to the outside with carved cornucopia pattern in an undulating design, with black enamel to the centre and the words 'IN MEMORY OF' in gold, with carved inscription to interior for 'Mary Dunnington Ob 5th Aug ae 64', with maker's mark BC & N for Barber, Cattle & North and York date letter for 1829, size M