1971  Rhymmoceratidae Ruzhentsev & Bogoslovskaia: 334.

A:   Conch form discoidal, vermicular, evolute, with wide
umbilicus.
B:   Ornamentation varies considerably.
G:   Ventral lobe rather narrow, with low median saddle; advanced
forms reach gastrioceran type of suture, but median lobe does not
exceed half of length of entire ventral lobe.

[Phylogenetic relationship with Nomismoceratidae probable].

Figs. TAX4838 A, B: Ophilyroceras tersum, C: Rhymmoceras
vermiculatum, D: R. spatiosum, E: R. perlatum, F: R. gracilentum
(sutures, from Ruzhentsev & Bogoslovskaia, 1971, fig.87).