Orthoceras regulare, from here.

Belongs within: Orthoceratidae.

Orthoceras is a Middle Ordovician genus of large orthocerid cephalopods.

Characters (from Sweet 1964): Slightly expanding, almost cylindrical orthocones or faintly exogastric cyrtocones; siphuncle empty, cylindrical, suborthochoanitic, subcentral to slightly ventral. Body chamber transversely constricted at mid-length and marked by single longitudinal dorsal and two longitudinal ventral depressions. Surface ornamented by network of fine lirae; internal surface faintly striated longitudinally, prominent conchal furrow on venter; muscle attachment dorsomyarian.

<==Orthoceras Bruguière 1789 [=Ortaoceras (l. c.), Orthoceros Brünnich 1771 (nom. rej. prop.)] S64
    |--*O. regulare (Schlotheim 1820) [=Orthoceratites regularis, *Orthoceros regularis] S64
    |--O. aciculoides Clarke 1885 P68
    |--O. alienoides Foerste 1928 P68
    |--O. angulatum S64
    |--O. asmodeus Clarke 1885 P68
    |--O. byronense Foerste 1928 P68
    |--O. caneyanum Girty 1909 P68
    |--O. carltonense Whitfield 1878 P68
    |--O. choctawense Girty 1909 P68
    |--O. clarki Cleland 1911 P68
    |--O. clarksvillense Foerste 1924 P68
    |--O. colon White 1874 P68
    |--O. crebriliratum Girty 1909 P68
    |--O. erraticum Foerste 1893 P68
    |--O. eurekensis Walcott 1884 P68
    |--O. filosum Clarke 1885 P68
    |--O. franklinense Miller 1894 P68
    |--O. guadelupense Girty 1908 P68
    |--O. imbricatum P68
    |--O. inceptum Foerste 1885 P68
    |    |--O. i. inceptum P68
    |    `--O. i. acceleratum Foerste 1893 P68
    |--O. indianum Firty 1909 P68
    |--O. junceum P68
    |--O. kingii Meek 1877 P68
    |--O. lambtonense Whiteaves 1898 P68
    |--O. lesueuri Clarke 1897 P68
    |--O. liaotungense Endo 1932 P68
    |--O. ludense H87
    |--O. magnichinense Endo 1932 P68
    |--O. mephisto Clarke 1885 P68
    |--O. moodiense Foerste 1928 P68
    |--O. multicameratum P68
    |--O. olorus P68
    |    |--O. o. olorus P68
    |    `--O. o. baffinense Schuchert 1900 P68
    |--O. ontario Clarke 1885 P68
    |--O. parlinense Williams & Breger 1916 P68
    |--O. porteri Schuchert 1900 P68
    |--O. princiana Williams & Breger 1916 P68
    |--O. randolphensis P68
    |--O. rectiseptatum Endo 1932 P68
    |--O. rogersensis Foerste 1914 P68
    |--O. rushensis P68
    |--O. scalariformis Schuchert 1900 P68
    |--O. shatzeri Foerste 1928 P68
    |--O. toyamai Endo 1932 P68
    |--O. tuba Girty 1911 P68
    |--O. tyronensis Foerste 1912 P68
    |--O. wapanuckense Girty 1909 P68
    |--O. whitfieldi Foerste 1928 P68
    `--O. wilmingtonense Foerste 1928 P68

*Type species of generic name indicated


[H87] Holland, C. H. 1987. The nautiloid cephalopods: a strange success story. Journal of the Geological Society 144 (1): 1-15.

[P68] Purnell, L. R. 1968. Catalog of the Type Specimens of Invertebrate Fossils. Part I: Paleozoic Cephalopoda. United States National Museum Bulletin 262: 1-198.

[S64] Sweet, W. C. 1964. Nautiloidea – Orthocerida. In Treatise on Invertebrate Paleontology pt. K. Mollusca 3. Cephalopoda – General Features – Endoceratoidea – Actinoceratoidea – Nautiloidea – Bactritoidea (R. C. Moore, ed.) pp. K216-K261. The Geological Society of America and the University of Kansas Press.

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