スッポン or Suppon in Latin letters.
Chinese softshell turtle. I have had it quite a few places, Kagurazaka Ishikawa was kind enough to serve it on turtle shaped plates just to remind us (will have to see if I can find a picture) Suiran in Kyoto brought a cleaned skeleton to the table so we could see what we were eating.

Suppon chawanmushi

Suppon skeleton