Sactorthoceratidae
The Sactorthoceratidae comprise Orthocerataceaen genera with a subcentral suborthochoanitic siphuncle composed of slightly expanded segments and free of organic deposits. The camerae (chambers) of the phragmocone (chambered portion) likewise have organic deposits that are typically retarded or sparse. Discussion The family, Sactorthoceratidae, was established by Rousseau Flower in 1946, based on the genus '' Sactorthoceras''. In 1962 Flower pointed out the problem of defining the Sactorthoceratidae based on ''Sactorthoceras''; there being three species groups within the genus: those with (1) short camerae and rather short tubular septal necks, (2) long camerae and slightly expanded siphuncle segments, (3) typically tubular siphuncle segments that are rapidly contracted at the septal foremina. In defining the Sactorthceratidae, the second group with slightly expanded segments was considered. However the type species ''S. goniaseptum'' belongs to the third group, with contrac ...
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Sigmocycloceras
''Sigmocycloceras'' is a Nautiloidea, nautiloid cephalopod discovered in the Middle Ordovician of Korea, said to be similar to ''Sactorthoceras'', and included in the Sactorthoceratidae, but unique in being longitudinally sigmoid and sculpted with transverse annuli. References

* Walter C Sweet 1964. Nautiloidea-Orthocerida; Treatise on Invertebrate Paleontology, Part K. Geol Soc of America and Univ. Kansas Press. Nautiloids {{paleo-cephalopod-stub ...
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