A shallow round vessel of bent wood is lined with bamboo leaves, filled with vinegared trout and rice, and pressed under a weight. When the lid comes off the leaves open outward like the spokes of a wheel and the pink of the fish shows underneath. You cut it in wedges, through the leaves, with the small plastic knife that comes in the box and is oddly satisfying to use.

Sales began in 1912. The company had been founded four years earlier, when Toyama station opened, and the sushi belongs to the railway as much as to the river. The picture on the wrapping paper, which most people would recognise before they recognised the name, was painted in 1965.

The fish was originally cherry salmon taken from the Jinzu River, which runs down out of the mountains through the city. Most of it now comes from Hokkaido. The river stopped supplying its own speciality some time ago; the shape and the vessel stayed exactly as they were.

The smell of bamboo has gone into the rice by the time you open it. The best moment is the opening, which you discover on the train, well before you have got it home. People buy a second one for the family and eat the first one standing on the platform.