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Murrayoceras
''Murrayoceras'' is a nautilid cephalopod included in the orthocerid family Baltoceratidae, widespread in the Middle Ordovician of North America, characterized by a depressed orthoconic shell with a subtriangular cross section and flattened venter and a proportionally large verntral siphuncle, 0.15 to 0.3 the dorso-ventral shell diameter.〔W. M. Furnish and Brian Glennister, 1964. Nautiloidea- Ellesmerocerida; Treatise on Invertebrate Paleontology, Part K. Geol. Soc. of America and Univ. Kansas Press〕 Septa are close spaced with sutures forming broad lobes on the upper flanks and ventral surface.
As originally perceived ''Murrayoceras'' included species differing in siphuncle profile.〔Rousseau H Flower, 1964. The Nautiloid Order Ellesmeroceratida (Cephalopoda). New Mexico Bureau of Mines and Mineral Resources Memoir 12.〕 Those in which the siphuncle segments are externally convex were redefined as Cartersoceras., leaving Murrayoceras with those having essentially straight, tubular, or slightly concave segments.
Murrayoceras has a ventral rod in the siphuncle,〔 putting it thereby in the rod-bearing Baltoceratidae, and closely related to ''Rhabdiferoceras'' and ''Cartersoceras'', among others. In some recent classifications however〔B. Kröger, et al.2007. Early orthoceratoid cephalopods from the Argentine Precordillera (Lower-Middle Ordovician). Journal of Paleontology 81(6):1266-1283 ()〕 ''Murrayoceras'' has been reassigned to the Sactorthoceratidae although Frey (1995)〔R. C. Frey. 1995. Middle and Upper Ordovician nautiloid cephalopods of the Cincinnati Arch region of Kentucky, Indiana, and Ohio. U.S. Geological Survey Professional Paper 1066P:1-126 ()〕 did retain the genus in the Baltoceratidae.
==''References''==
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