These are Ultegra 54mm length, aluminum, cartridge brake shoes that have toe-in adjustment built into the shoe.  The black pads are alright for wet and dry but when they wear out replace them with the better kool-stop pad inserts.

Neat itty bitty bumpers on the wheel-guide/heat-sink fins to prevent rim scraping and scratching when the pads are close to being all worn out.

Perfect upgrade for CX50 cantilever brakes.

Official Shimano name: BR-6700 R55C3