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|regnum = Animalia |phylum = Mollusca |classis = Cephalopoda |subclassis = Ammonoidea |ordo = Ceratitida |superfamilia = Arcestaceae |familia = Arcestidae |genus = ''Arcestes'' |genus_authority = Suess (1865) |subdivision_ranks = Species 〔(Paleobiology Database - Arcestes ). 2014-05-29.〕 |subdivision = * ''A. (Pararcestes)'' * ''A. andersoni'' † Hyatt and Smith 1905 * ''A. intuslabiatus'' † Mojsisovics 1873 * ''A. megaphyllus'' † Beyrich 1864 * ''A. priscus'' † Waagen 1879 * ''A. syngonus'' † Mojsisovics 1873 }} ''Arcestes'' is an extinct ammonite cephalopod genus belonging to the Ceratitida. ==Description== Their shells were broad and rounded, giving them an almost spherical appearance. Unlike many other ammonites, the shells of ''Arcestes'' lack keels that would otherwise stabilize them while swimming. Because of this, some paleontologists have suggested that they were bottom-dwelling crawlers. The shell of ''Arcestes'' is globular or subglobular with periodic narrow transverse constrictions in internal molds due to periodic internal transverse ridges (variaces) in the shell. The suture is ammonitic with complexly subdivided elements. The ventral lobe is subdivided by a low median saddle. Lateral lobes and saddles have generally triangular outlines but are deeply embayed by strong projections forming tree-like patterns. They form a series diminishing in size and complexity in a rather straight line going from the venter to the umbilicus in the middle of the shell. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Arcestes」の詳細全文を読む スポンサード リンク
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