It's been a long time since you posted and you may already have this information. I came across this because I have a Cahill connection also.
This is a "missing friends ad" from the Boston Pilot.
DANIEL LYNEHAN OF DANIEL & Garrett LYNEHAN, of the towns of Knuckeree and Williamstown, co Cork, who came to this country 2 to 3 years ago. Their niece, Honora Cahill has arrived in the ship Ontario, and wishes to hear from them. Information will be received by her at 335 First Avenue, New York. Dec 16, 1854
Irish Immigrant Advertisements Placed in The Boston Pilot 1831-1920, Volume III: 1854 - 1856, edited by Ruth-Ann M. Harris and B. Emer O'Keeff