''Arnioceras'' is an extinct genus of large, evolute, discoidal

ammonite Ammonoids are a group of extinct marine mollusc animals in the subclass Ammonoidea of the class Cephalopoda. These molluscs, commonly referred to as ammonites, are more closely related to living coleoids (i.e., octopuses, squid and cuttlefish) ...

from the Lower

Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The J ...

. The shell is normally coiled so that all whorls are exposed. Sides bear strong sharp ribs that are straight until reaching the ventrolateral edge where they swing forward and fade. The rim (venter) is keeled and free of grooves. ''Arnioceras'', named by

Alpheus Hyatt Alpheus Hyatt (April 5, 1838 – January 15, 1902) was an American zoologist and palaeontologist. Biography Alpheus Hyatt II was born in Washington, D.C. to Alpheus Hyatt and Harriet Randolph (King) Hyatt. He briefly attended the Maryla ...

, is included in the arietitid family of the

Psiloceratoidea Psiloceratoidea is a superfamily of Early Jurassic ammonoid cephalopods proposed by Hyatt in 1867, assigned to the order Ammonitida. They were very successful during Hettangian and Sinemurian. Last of them, family Cymbitidae and genera ''Hypoxy ...

, an ammonitid supefamily. Its distribution is fairly worldwide, having been found in Europe, south Asia, and North and South America.

References

;Notes ;Bibliography * Jurassic ammonites Jurassic ammonites of North America Ammonitida genera Early Jurassic ammonites Hasle Formation Taxa named by Alpheus Hyatt Fossil taxa described in 1897 Arietitidae {{Ammonite-stub