Placenticeras

Placenticeras, named by Fielding Bradford Meek, 1870, is the type genus for the Placenticeratidae, a family that is part of the Hoplitoidea, a superfamily of the Ammonitida. ==Description==

Placenticeras has a very involute shell with slightly convex sides and a very narrow venter. Side are smooth or with faint sinuous ribs. Early whorls have umbilical tubercles that in later whorls appear higher on the sides. Earlier whorls normally have lower and fine upper ventrolateral clavi. Ornament weakens in the adult and the last whorl may be smooth. The suture is with numerous adventitious and auxiliary elements, with saddles and lobes that are much frilled. ==Species==

The genus contains the following species: • Placenticeras bidorsatum • Placenticeras costatum • Placenticeras cumminsi • Placenticeras fritschi • Placenticeras grossouvrei • Placenticeras intercalare • Placenticeras kolbajense • Placenticeras maherndli • Placenticeras mediasiaticum • Placenticeras memoriaschloenbachi • Placenticeras meeki • Placenticeras orbignyanum • Placenticeras paraplanum • Placenticeras placenta • Placenticeras polyopsis • Placenticeras pseudoplacenta • Placenticeras semiornatum • Placenticeras syrtale (syn. Stantonoceras pseudocostatum) • Placenticeras tamulicum • Placenticeras vredenburgi • Placenticeras whitfieldi == Gallery ==

File:Placenticeras costatum, Cretaceous, Pierre Shale Formation, Cheyenne River, Pennington County, South Dakota, USA - Houston Museum of Natural Science - DSC02011.JPG|P. costatum, Pierre Shale Formation, South Dakota File:Placenticeras placenta (fossil ammonite) (Upper Cretaceous; western North America) 1.jpg|P. placenta with mosasaur bite marks File:Placenticeras meeki, Late Cretaceous, Pierre Shale Formation, Rosebud County, Montana, USA - Houston Museum of Natural Science - DSC01924.JPG|P. meeki showing sutures File:Placenticeras intercalare at the American Museum of Natural History.jpg|P. intercalare ammolite, Bearpaw Formation, Alberta, Canada File:Placenticeras UMMNH.jpg|P. whitfieldi with mosasaur bite marks File:Placenticeras sp. (fossil ammonite) (Pierre Shale, Upper Cretaceous; Meade County, South Dakota, USA) 1.jpg|Placenticeras sp. showing sutures. Pierre Shale, Upper Cretaceous; Meade County, South Dakota (USA) ==References==