Acrimeroceras is an oxyconic Devonian

Devonian

The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...

 gonitite and one of three genera included in the subfamily Paratornoceratinae

Paratornoceratinae

Paratornoceratinae is a subfamily of oxyconic dimeroceratids included in the order Goniatitida, a group of Paleozoic ammonoids, which have closer affinity to living coleoids than to Nautilus....

. The others being Paratornoceras and Paratoceras

Paratoceras

Paratoceras is a medium-sized extinct genus of Artiodactyla, of the family Protoceratidae, endemic to North America from the Miocene epoch, 16.3—15.97 Ma, existing for approximately .-Taxonomy:...

or ex Polonites.

Acrimeroceras has a shell like that of Paratornoceras with biconvex growth lines and constrictions and simple dorsal lobe. The adult shell is extremely compressed, smooth, oxyconic to lanceolate in section. Early growth stages are depressed, subglobular, smooth or ribbled, with an open umbilcus and rounded to suboxyconic venter, which sharpens relatively early during ontogeny. Sutural elements in general are broadly rounded except for the lateral lobe which is pointed and asymmetric.