Covered under Edwin McClain’s December 1928 US patent, this Hagen sand wedge has a dramatically curved face and a large, broad sole.  Bobby Jones even used one of these in the 1930 British Open.  In 1931 the USGA adopted a new regulation that made any club with a concave face non-conforming.  Consequently, Hagen stopped producing its concave sand wedge.

This example appears unused.  The original shaft still has its original decal, and the Hagen name can still be seen stamped into the original grip. Hagen concave sand wedges can be found, but you won’t find a nicer example that this one.

TCA2 Vol. 1 p. 283-284