Jianzhan from the late Song Dynasty.
This bowl is known as a jianzhan, or 建盞 ／ 建盏 in Chinese. Specifically, it is called a hare's fur jianzhan, or 兔毫盞 ／ 兔毫盏, thus named for the appearance of rust-coloured streaks on the glaze, which resemble the fur of the hare.
I should probably write a proper post briefly introducing jianzhan and tenmoku in general — by far my favourite family of ceramic vessels — but the topic is very complex and I'm not sure if I'm ready to broach it yet.
Meanwhile, here are some photos showing some details of the tea bowl.