The two coped attendants carrying the gremial before the prelate (which looks to be like the future John XXIII) is what one would have seen in the pontifical liturgy of the Lyonese rite.
Incidentally, the vested priests in chasuble is likewise a feature of the pontifical Lyonese liturgy.
The spanish gremial:http://liturgia.mforos.com/1767119/8484216-el-gremial/#90185444http://liturgia.mforos.com/1767119/8484216-el-gremial/#87322026
it is a picture from a rare and indeed unique Liturgical form of the Mass known as the Rite of Lyon. the veil being carried before the bishop is the gremial. The Rite of Lyon was one of the few occasions in which you would see additional priests vested for Mass as well as the Celebrant.
It is very interesting that in the rite Lyon also used the processional gremial, as in some parts of Spain.
Rite de Lyon (see of the "primat des Gaules" in France) celebrated by Nuncio Rocalli, holding the "gremial" during the entrance procession ; this rite requires 12 priests ; dalmatics of Lyon have a collar, the only one of that kind in France.
All flushed down the toilet thanks to Vatican II! Makes for purty pictures though :)