| Named By: | McLearn in 1927 |
| Time Period: | Jurassic |
| Location: | Australia - Newmarracarra Limestone Formation. Possible also North America |
| Size: | Unavailable |
| Diet: | Carnivore |
| Fossil(s): | Many individuals represented by fossilised shells |
| Classification: | | Mollusca | Cephalopoda | Ammonoidea | Ammonitida | Stephanocerataceae | Otoitidae | |
Zemistephanus is an extinct ammonite genus from the middle Jurassic of western North America and Western Australia, named by McLearn 1927. Zemistephanus is included in the sephanoceratoid family Otoitidae, which are characterized by shells that begin as barrel-shaped cadicones but which become planulate later in life. Body chambers are reduced in size and are excentric. Similar genera are Pseudotoites and Emileia