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Amaltheidae is a family of eoderoceratacean ammonitids from the Lower Jurassic consisting of genera characterised by stigated discoidal oxycones—narrow involute shells with narrowly rounded to angular venters that bear a series of grooves, or ridges, along broad flanks, which according to the Treatise L, 1957, evolved into strongly ribbed planulates (discoidal evolute shells) with quadrate whorls, typically with crenulated keels; involving all together four genera. Donovan in Donovan ''et al.'' (1981) retains the Amaltheidae in the sense of Arkell, ''et al.'' 1957, as shown in the Treatise but synonymizes ''Pseudoamaltheus'' with ''Amaltheus'', (a subgenus in the Treatise), reducing the number of valid genera to three. These are ''Amaltheus'', ''Amauroceras'', and ''Pleuroceras''. ''Amaltheus'' is oxyconic, keeled, strigated, and ribbed on the outer flanks. ''Amauroceras'' is smooth, compressed, without ribs or stigation, and the keel is reduced. ''Pleuroceras'' has a planulate shell with a quadrate whorl section, bearing strong radial ribs ending in ventro-lateral tubercles. The venter is tabulate with a strong serrated keel. The Amaltheidae are derived from the Liparoceratidae and have a principally boreal distribution ==References== * Arkell, ''et al.'', 1957. Mesozoic Ammonoidea. Treatise on Invertebrate Paleontology, Part L; Geological Society of America and University Kansas press. * Donovan, Collomon,& Howarth. Classification of the Jurassic Ammonitina, in The Ammonoidea, M.R. House and J.R. Senior (eds) Academic Press 1981. Systematics Association Special Volume. 18. () 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「Amaltheidae」の詳細全文を読む スポンサード リンク
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