I find it somewhat odd that the date given for the "Fête de Saint Jacques" is July 11 since the traditional Catholic feast day for St. James is July 25.
I can't readily locate any arms attributed to St. James, but many towns, cities, and churches named for him include scallop shells in their arms or other insignia. For example, St. James Episcopal Church in Leesburg, Virginia, has adopted the arms
Chequy Or and Azure on a chief ermine a cross gules charged with an escallop of the first. Their explanation of the arms leaves a little to be desired, especially their description of Azure, but it is an excellent use of heraldry in the States.
http://www.stjamesleesburg.org/coatOfArms.asp