This piece is a very interesting, quality specimen.  It was found in the Fox Hills Formation in South Dakota.  I'm undecided at what it is exactly when looking in my fossil book.  It is not a Belemnite.  The closest thing that it appears to be is a possible Endoceras, Bactrite, or Dentalium.  If you happen to know, please message me!  It is a very high quality, beautiful piece.  It measures approximately 2.5" in a matrix that is about 3.5".  The matrix it sits in is highly fossiliferous with impressions of a scaphite and has little clam companions and misc.  It is very fun to look at and now I want to give someone else the chance to enjoy this piece like I have.  Thanks so much for looking and have a great week!