Hi
You're very sparse with your info. Your posting suggests you have Census info + possibly ages at death of Richard and Mary.
There are a couple of this name at Pantglas, Maentwrog, plus 2 sons, John and Richard, and 2 daughters. Is this the family your referring to? In Cambrian News, 12 July 1901:
MAENTWROG.
Success - Mr Wm Griffith, son of Mr Richard Griffith, Pantglas, is placed high in the list of succesful candidates in the Glamorganshire C.M. annual examination.
Gwynedd Family History Society have published a booklet of the Memorial Inscriptions, ref.: M222.
Emyr