Anapachydiscus is an extinct cephalopod genus from the Upper Cretaceous, Coniacian

Coniacian

The Coniacian is an age or stage in the geologic timescale. It is a subdivision of the Late Cretaceous epoch or Upper Cretaceous series and spans the time between 89.3 ± 1 Ma and 85.8 ± 0.7 Ma...

 - Maastrichtian

Maastrichtian

The Maastrichtian is, in the ICS' geologic timescale, the latest age or upper stage of the Late Cretaceous epoch or Upper Cretaceous series, the Cretaceous period or system, and of the Mesozoic era or erathem. It spanned from 70.6 ± 0.6 Ma to 65.5 ± 0.3 Ma...

 of Europe, Africa, Madagascar, S.India, N Z, Calif. Mexico, Argentina, and the antarctic belonging to the ammonoid family Pachydiscidae

Pachydiscidae

Pachydiscidae comprise a family of middle and upper Cretaceous ammonites which makes up part of the Desmocerataceae.Pachydiscidae are of moderate to large size, evolute to rather involute, and vary in section from inflated and depressed to high-whorled and compressed...

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Anapachydiscus has a rather involute shell with a broad to moderately compressed whorl section. Early whorls smooth, intermediary develop straight or slightly curved, radial ribs that thicken toward the umbilicus. Outer whorls may again be smooth, or have coarse ribs so as to resemble Eupachydiscus

Eupachydiscus

Eupachydisus is a large, coarse-ribbed Pachydiscid ammonite genus from the Upper Cretaceous, found in Coniacian to Campanian age strata in Europe, Madagascar, Japan, and British Columbia....

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References

• Treatise on invertebrate Paleontology, Part L, Mollusca 4. Mesozoic Ammonoidea. Geological Society of America and Univ. Kansas Press (1957)
• Anapachydiscus-Paleodb 5/02/11