A Mass of Thanksgiving in which John Cardinal Krol, Archbishop of Philadelphia, was the principal celebrant, was held yesterday in the Cathedral of St. Catharine of Siena, Allentown, in observance of the silver anniversary of the establishment of the Diocese of Allentown.

More than 50 concelebrants participated in the ceremony, including the Most Rev. Pio Laghi, Apostolic Pro-Nuncio to the United States, and the Most Rev. Thomas J. Welsh, Bishop of Allentown, and hie predecessor, the McShea.

Hundreds of priests, religious and lay people representing all 156 parishes of the diocese were in attendance.

Bishop McShea served as head of the diocese since its inception until retiring three years ago, at which time Bishop Welsh, a Weatherly native, was named to fill the position.