|
''Albertoceras'' is an Early Ordovician ellesmoeroceratid genus with a small, slender, orthoconic to slightly endogastric shell; some even tiny. The cross section is strongly compressed so as to make the height proportionally notably greater than the width. The sutures, marking the edges of the septa, have broad, shallow, lateral lobes. The siphuncle, which seems to lack diaphragms, lies close to the venter. ''Albertoceras'' differs from ''Ectenolites'', which it closely resembles in the early, or juvenile, portion, in a having a short living chamber that narrows toward the aperture and a convex dorsal profile in the adult portion. The ventral profile remains straight throughout. ''Albertoceras walcotti'', the type species, and ''A. gracillimum'' are both from the Mons Formation of Alberta. ''A. staufferi'' is from the Tanyard Formation of Texas and ''A. clelandi'' is from the Tribes Hill Limestone of New York. ==References== * R.H. Flower, 1964. The Nautiloid Order Ellesmeroceratida (Cephalopoda). Memoir 12. New Mexico Bureau of Mines and Mineral Resources, Socorro NM. * W.M Furnish & Brian F. Glenister, 1964. Nautiloidea - Ellesmerocerida. Treatise on Invertebrate Paleontology, Part K. Geological Society of America and University of Kansas Press. 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「Albertoceras」の詳細全文を読む スポンサード リンク
|