The following genealogy is taken from a text within the O Clery Book of Genealogies  a genealogical collection compiled in the seventeenth century. The names of most of those appearing in the terminal generations have been omitted for reasons of clarity. The numbers in square brackets are the paragraph numbers in the published edition. Names have been standardised.
An Oifistel |_______________________________________________________________________________________________ | | | Felim Giolla bui Donncha |___________________________________________ | | | | | | Cumhai Ruairi Felim Niall | | | | Felim Domhnall find Aedh Glasne An Airchinnech | | | |______________________________ |____________________________ | | | | | | | | | Risdeard Brian dubh Maghnus bui Niall carrach Torlach Brian Eoghan |_______ | | | | | | | | | | | | | | Felim Brian Domhnall Padraig Seamus Domhnall 2 sons Conor | | | | |______________ |  | | | | | | | | | Ruairi Emann Brian carrach Torlach Donncha garbh Sean caoch Maghnus 1 son | | | | | | |  2 sons 2 sons 1 son 1 son 2 sons Conor Ruairi      An Brathair | + 4 sons 1 son  
Note that An Oifistel is an individual described as holding the office of an oifistel ('the official') whose personal name has not survived. The official was a person appointed to the ecclesiastical office of vicar-general in temporals who as principal judicial and administrative officer of the bishop presided at the ecclesiastical consistory court. To the extent that the standard generation length of thirty three years from the death of Domhnall of Cameirge places An Oifistel alive circa 1440 it would appear that his advancement may have been due to the influence of Domhnall MacLochlainn who (as given elsewhere) was a canon in the chapter of Derry cathedral in 1397 and who held the rectory of Moville as prebend until his death 1397x1412. His great-grandson Felim is described as holding the office of an airchinnech ('the superior'/anglicised spelling 'erenagh') and so it seems that his descendants continued to pursue opportunities within the Church administration. Erenaghs were relics of the old ecclesiastical order being superiors of defunct ecclesiastical communities whose lands had transferred to episcopal control following the reforming synods of the twelfth century. The office survived in titular form attached to a chief tenancy in these episcopal lands held by right of descent within a family and the holders of the office retained a sense of being ecclesiastics in minor orders, an obligation to provide hospitality to travellers and a fluency in Latin . An English survey of 1607 preliminary to the disposession of the Catholic dioceses of western Ulster records a Cornelius and a Donatus MacLochlainn as erenaghs of lands in Grallagh to the east of Trawbreaga bay on the north coast of Inishowen . These can readily be identified as latinisations of the names of two people appearing in the genealogy, being Conor described as an brathair ('the brother') together with his uncle Donncha garbh. At an English inquisition held in Lifford in 1609 this branch of the family were referred to as the Clanloughlangrillies  which would appear to be an anglicisation of Clann Lochlainn Grealligh ('MacLochlainn family of Grallagh') in which the placename element greallach ('marsh') is declined into genitive form. From a review of the archaeological remains in the area it would seem that this family occupied a church site at Templemoyle equidistant between the modern towns of Culdaff and Malin at which there are remains of a small D-shaped structure resembling a fort . The same inquisition records a Maghnus MacLochlainn as erenagh of lands in Moville and he can readily be identified in the genealogy as Maghnus of paragraph 334. A MacLochlainn was also erenagh of lands in Derry. At an English inquisition held in Derry in 1609 it was stated that :
within the said iland of Derry there were twoe herenaghes belonginge to the late abbot of Collumkill, the one called Loughlina, within the dioces of Derry, and thother called Oderry, within the dioces of Rapoe
Loughlina is clearly an anglicisation of Lochlannach ('a MacLochlainn') and having already identified the MacLochlainn erenagh family of Grallagh and the MacLochlainn erenagh family of Moville as falling within the sub-branch descending from Domhnall find it follows that the MacLochlainn erenagh family of Derry falls within the sub-branch descending from Felim, the only person actually described in the genealogy as holding the office of erenagh. The inquisition proceeds to give a couple of clues as to the extent of the MacLochlainn erenagh lands in Derry:
the said lord busshop of Derry is, and his predecessors have, tyme out of mynde, bene possessed of one orchard or parke, lyinge on the east syde of the great forte in the said iland of Derrye, payinge thereout yerely unto the erenagh Laghlina, ten white groats per annum
the grounde and land whereon the old castle called O’Donnels castle was built, within the lower forte of the citie of Derry, was formerly bought by O’Donnel of the erenagh Laghlinaghe as beinge pcell of his herenagh land
In maps of the seventeenth century a castle occupied the site of the present Tower Museum so it would appear that the MacLochlainn erenagh held the northern part of the island of Derry and with it the churchlands extending across what are now the northern suburbs of the city. Unfortunately, a troubled history has ensured that no medieval structures survive in Derry and so we cannot identify this family with any particular site.