NARA Pension Index Card
Here's the index record that references Mary Kenna's application to receive a dependent pension with regard to her son William Kenna Jr. General Affidavit of James Kenna/Kana Jr. 1 May 1878
In this document James Kenna Jr. states that he is a cousin of William Kenna Jr. He lists the ages of Mary and William Kenna Sr.'s children. Birth Affidavit for William Kenna Jr.
Mary O'Rourk (?) and James Kana state that they (or just he) were present at the birth on 25 Sep 1842. The witnesses are Patrick Murry and David Mahony.