Discovery of specimens of Glaphyrites (Goniatitina: Gastriocerataceae) without any ma-
  trix inside the shell permits a three-dimensional view of the internal features.  The speci-
  mens were found in phosphatic nodules from the Upper Carboniferous (Missourian Stage
  = lower Stephanian) of Oklahoma.  Although the original shell microstructure is not pre-
  served, the internal features are well exposed.  The caecum is elliptical in outline in the
  median plane (= the plane of symmetry) and is attached to the inside surface of the initial
  chamber by a short, curved prosiphon.  There is a single, elongated muscle scar on the in-
  side surface of the initial chamber just above the flange.  A ridge occurs along the line of
  attachment of the proseptum on its adapical side.  The distance between the proseptum and
  the second septum in the median plane is much smaller than that between the second and
  third septa.  The proseptum has a short septal neck that is projected both adorally and
  adapically.  The second septum is achoanitic or possibly has a short retrochoanitic neck.
  The siphuncle is generally ventral throughout ontogeny, although it extends straight across
  the chamber in a few chambers in the first whorl.  The ammonitella does not show any mi-
  cro-ornamentation but lirae appear immediately adoral of the primary constriction.  The
  presence of such features as the muscle scar on the inside surface of the initial chamber
  just above the flange and the ridge along the line of attachment of the proseptum on its
 adapical side are similar to features observed in some Mesozoic ammonoids (e.g., in the
Ancyloceratina) and may indicate similarities in embryonic development.