Your ammonite probably is...
Manticoceras
Suture: Goniatitic
Manticoceras was fairly narrow. Its aperture was triangular or elliptical. It had an open umbilicus. It had a curved suture with 3 lobes. Its siphuncle ran along its venter.
"By Ghedoghedo (Own work) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons" "https://commons.wikimedia.org/wiki/File%3AManticoceras.jpg"
