On June 20 the Most Rev. Mark A, O’Toole (59) a priest of the Archdiocese of Westminster and formerly the Bishop of Plymouth was installed as the 10th Metropolitan Archbishop of Cardiff in Wales. On June 23 this same prelate was also installed as the Bishop of Menevia in Wales. The two dioceses remain separate for the present but are joined in a personal union through having a single bishop.
The arms he has now assumed since his move to Wales, which are different from those he bore as Bishop of Plymouth incorporate the pall (pallium) as a charge on the shield rather than the less-than-ideal attempt to include it in the achievement as an external ornament. The latter has become popular in recent years but is really a poor design decision that never quite works.
For reasons I do not know the Archbishop has chosen not to impale his personal arms with those of the Sees. Perhaps it is because there are two different Sees. Quartering would have solved that issue, however.

In Italy those “personal unions” for dioceses appear more and more. In most situations they are a prediction for a real junction between two dioceses.
The sees, in common with all Roman Catholic sees in England, do not possess arms.