Fungus on Walnut trunk

This fungus was found on a Walnut trunk which had been felled because the tree was 'dead'.   Although some of it sounds hollow to the knock, clearly not all of it is yet dead.   I would welcome help with the identification of the fungus, and would be interested to know how particular it is to Walnut.   It was wonderful to find the fungus in such good condition, particularly as these were the only two outcrops.