Breviconic Oncoceratidae

Breviconic Oncoceratidae comprise genera included in the family Oncoceratidae known from generally short, i.e. breviconic and often exogastrically curved shells. They are considered oncoceratids (nautiloid order Oncocerida) on the basis of having typically empty siphuncles ventral of the center that may be suborthochoanitic and tubular in the early growth stage and cyrtochoantic with expanded segments in later growth stages or entirely. Connecting rings are thin. Breviconic oncoceratids differ from slender oncoeratids only in the matter of relative length. Inclusion is based on descriptions and illustrations in Sweet 1964 on the Oncerida in the Treatise on Invertebrate Paleontology, Park K.

Included genera

Breviconic oncoceratid genera include:

Oncoceras; compressed, curved brevicones, M-U Ord, N Am., Eu.
Beloitoceras; compressed, curved brevicones, like Oncoceras, M-U Ord, N Am., Eu.
Metarizoceras; slightly curved, compressed, rapidly expanding brevicons, M Sil. N Am.
Neumatoceras; compressed brevicones with maximum height behind posterior end of body chamber, M-U Ord., N Am., Eu.
?Vaupella; depressed, cyrtoconic brevicones with large ventral cytrochoanitic siphuncle, otherwise with characters of the family.

References

• Walter C.Sweet, Nautiloidea-Oncocerida, Treatise on Invertebrate Paleontology, Part K, Geological Society of America and University of Kansas press, 1964 (K283-K290), Teichert C and Moore R.C (Eds).