K. Tanabe, C: Kulicki, N.H.Landman & R.Mapes:
 
  Abstract.  The ornamentation and dorsal wall structure of Vidrioceras (Cycloloboidea, Goniatitina)
  in the early ontogenetic stage are described on the basis of specimens from the Upper
  Pennsylvanian in Kansas, USA.  The exposed surface of the embryonic shell is smooth, without any
  trace of ornamentation or growth lines.      Regularly spaced lirae abruptly appear on the early
  postembryonic shell just adoral of the primary constriction.  The inner surface of the dorsal wall
  in the embryonic and early postembryonic stages exhibits a distinct ornament consisting of evenly
  spaced, longitudinal ridges, which are replaced adorally by the typical wrinkled ornament in the
  subsequent stage.     Our observations are in accord with those of goniatites from the Upper
  Carboniferous Buckhorn Asphalt of  Oklahoma, suggesting that in the Goniatitina,  the outer surface
  of the embryonic shell is smooth.      Comparison with the embryonic shell formation of extant
  Nautilus suggests that in the Goniatitina, the embryonic shell was uniformly secreted by the shell
  gland on the posterior side of the embryo.