OscarBrownbread
Oh excellent, you are right that Calvy and Thulis are family names in the area! Good to know! http://askaboutireland.ie/griffith-valuation/index.xml?action=doNameSearch&Submit.x=0&Submit.y=0&Submit=Submit&familyname=calvy&firstname=&baronyname=&countyname=MAYO&unionname=&parishname=

The Irish name is "Ball Dumha Cinn Aille". My Irish is bad but I am wondering about Ball, as in 'part of'. I think they are somehow linked. 

Comparing TD areas is another good tip, thanks. I will hopefully correct the townland border soon and leave it at that for now.