Body: Ostrich's herl ribbed with sliver twist, and a black cock's hackle over all.
I tied it on a Mustad 9671 #12 with Black Monocord...

Hofland didn't specify what color ostrich, but Pulman in the Vade-Mecum of Fly-fishing for Trout 1841 used black ribbed by gold or silver twist.
My thanks again to Andrew Herd!