The cut is 'plat nerveux' and was purchased at a Parisian (French) market. It is beef, long-ish, round (like a sausage), and boneless. The meat is deeper red than most beef cuts I am used to. Deep red, but not liver or other organ color.
This cut is not even listed on https://tasteofsavoie.com/2018/10/23/french-meat-cuts/