In the first instance, I would check if a parish is also recorded in the address information for your ancestor.
Inconsistency in spelling of place names (and surnames) is well known to those who have conducted research into their Irish family history. Place names, originally in Gaelic, were anglicised from the17th century, by settlers with little knowledge of the Irish language. This resulted in many different spellings of the same place name. An ‘official’ and standardised spelling of townland names for all Ireland was established, by1842, by the Ordnance Survey and published in the Townland Index and on Ordnance Survey maps.
Bellemamaugh, County Antrim is quite likely a corruption/misspelling of a townland name that is currently ‘disguised’. For example, the parish of Ballymoney, County Antrim contains townlands that are now 'officially' spelt as Ballynamenagh North and Ballynamoney,
https://www.johngrenham.com/c_parish/c_parish_main.php?civilparishid=276&civilparish=Ballymoney&CountyMap=