The Allotrioceratidae is a family of Middle Ordovician fossils, established by Rousseau Flower, 1955, originally including ''

Allotrioceras ''Allotrioceras'' is a tubular fossil from the Middle Ordovician of the state of New York, collected by Rousseau H. Flower; included by him in the Endocerida and placed in a new family, the Allotrioceratidae. ''Allotrioceras'' is characterized ...

'' and '' Mirabilocras'', assigned inferentially to the

Endocerida Endocerida is an extinct nautiloid order, a group of cephalopods from the Lower Paleozoic with cone-like deposits in their siphuncle. Endocerida was a diverse group of cephalopods that lived from the Early Ordovician possibly to the Late Silu ...

and known only from structures interpreted as siphuncles. Later ''

Williamsoceras Williamsoceras is an endocerid that Rousseau Flower (1968) added to his Allotrioceratidae (Flower 1955) on the basis of having a vertical partition within the siphuncle, known as a ventral process, with inter-connecting tubule-like structure ...

'', '' Cacheoceras'', and '' Perkinsoceras'' (Flower 1968, 1976) were added. Similar ''Allotrioceras'' and ''Mirabiloceras'', known only from the Chazyan (upper lower Middle Ordovician) of New York, are tubular organisms with complex interiors somewhat resembling that of the Endocerida. The later added ''Williamsoceras'', ''Cacheoceras'', and ''Perkinsoceras'' are true endocerids as indicated by their cylindroid shells, phragmocones, and siphuncles. ''Williamsoceras'' and ''Cacheoceras'' are from the Whiterockian stage (lower lower Middle Ordovian) of Utah. ''Perkinsoceras'', which appeared somewhat later, is from the Chazyan of New York, like ''Allotrioceras'' and ''Mirabilioceras'' but rather distinct from either. The Allotrioceratidae of Rousseau Flower (Flower 1955) is defined on the basis a structure within the siphuncle, assumed or real, known as an infula that consists of a thin dark, arcuate or curved, line with dark spots interpreted as endosiphuncular tubules. ''Allotrioceras'' and ''Mirabilioceras'' also have internal subdividing structures that somewhat resemble the longitudinal processes found the siphuncles of some endocerids including ''Williamsoceras'', ''Cacheoceras'', and ''Perkinsoceras''. The holotypes of ''Allotrioceras'' and ''Mirabiloceras'' are housed in the collections of the

New Mexico Museum of Natural History and Science The New Mexico Museum of Natural History and Science is a natural history and science museum in Albuquerque, New Mexico near Old Town Albuquerque. The Museum was founded in 1986. It operates as a public revenue facility of the New Mexico Departmen ...

in Albuquerque, New Mexico.

''References''

*Rousseau H Flower, 1955. Status of Endoceroid Classification. Journal of Paleontology Vol 29, no 3, May, 1955. * __ 1968. Some Additional Whiterock Cephalopods. New Mexico Bureau of Mines & Mineral Resources, Mem 19, pt 2. * __ 1976. Some Whiterock and Chazy Endoceroids, New Mexico Bureau of Mines & Mineral Resources, Part II, Mem 28, {{Taxonbar, from=Q16974086 Ordovician molluscs Prehistoric cephalopod families Middle Ordovician first appearances Middle Ordovician extinctions Taxa named by Rousseau H. Flower