Aturia_Angustata in the sunshine

Aturia Augustata is an Eocene Nautiloid from Lincoln Creek Formation, Grays Harbor County, WA, USA .

Sutures (or suture lines) are visible as a series of narrow wavy lines on the surface of the shell, and they appear where each septum contacts the wall of the outer shell. The sutures of the nautiloids are simple in shape, being either straight or slightly curved.
This is different from the "zigzag" sutures of the goniatites and the highly complex sutures of the ammonites.