Here is the marriage record from www.rootsireland.ie/ but it has very little info!:
Date of Marriage:11-Dec-1878
Parish / District:BALLYNAKILL
County:Co. Galway
Husband
WifeName:JohnLyden
MaryMullinAddress:Not Recorded
BanoguesDenomination:Roman Catholic
Roman CatholicOccupation:
Age:
Status:
Husband's Father
Wife's FatherName:Not RecordedLyden
Not RecordedMullinAddress:
Denomination:
Occupation:
Husband's Mother
Wife's MotherName:Not RecordedNot Recorded
Not RecordedNot RecordedAddress:
Denomination:
Occupation:
Witness 1
Witness 2Name:MichaelMullin
HonorMullin
Mary's Baptism:
Name:Mary MullenDate of Birth:
Date of Baptism:14-Jan-1849Address:LetterdeenParish/District:CLIFDENGender:FemaleCountyCo. Galway
Denomination:Roman Catholic
Father:Peter MullenMother:Mary FlahertyOccupation:
Sponsor 1 /
Informant 1:Peter MullenSponsor 2 /
Informant 2:Bridget King
There are quite a few John Lydon baptisms in and around 1851 in Galway so hard to tell which is yours.
IF he was also from Ballynakill, this is the only one from there:
Name:John LydonDate of Birth:
Date of Baptism:05-Apr-1843Address:DerrinverParish/District:BALLINAKILLGender:MaleCountyCo. Galway
Denomination:Church Of Ireland
Father:James LydonMother:Mary LydonOccupation:Labourer
However the marriage record has him as RC. There are none from Ballynakill R C parish & no records from Ballinahinch on rootsireland.ie
IF he was born in Clifden like Mary:
Name:John LydenDate of Birth:
Date of Baptism:18-Sep-1851Address:Not RecordedParish/District:CLIFDENGender:MaleCountyCo. Galway
Denomination:Roman Catholic
Father:Thomas LydenMother:Anne ConeelaOccupation:
Sponsor 1 /
Informant 1:John PrendergastSponsor 2 /
Informant 2:Mary Anne Lyden
You might try Griffiths Valuation & the Tithe Applotments (both free) to see where the Lydons & Mullens were in earlier years
Col