''Eotripteroceras'' is a smooth-shelled michelinocerin orthocerid from the middle

Ordovician The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya. ...

of the state of New York. The shell of ''Eotripteroceras'' is a depressed orthocone with the underside (the venter) flatter than the upper (the dorsum). The

siphuncle The siphuncle is a strand of tissue passing longitudinally through the shell of a cephalopod mollusk. Only cephalopods with chambered shells have siphuncles, such as the extinct ammonites and belemnites, and the living nautiluses, cuttlefish, and ...

is below the center -as viewed in horizontal orientation- and is cylindrical in form. Both siphuncle and chambers are empty.

''References''

* Sweet, Walter C. 1964. Nautiloidea-Orthocerida.

Treatise on Invertebrate Paleontology The ''Treatise on Invertebrate Paleontology'' (or ''TIP'') published by the Geological Society of America and the University of Kansas Press, is a definitive multi-authored work of some 50 volumes, written by more than 300 paleontologists, and co ...

, Part K. Geological Soc of America, and Univ Kansas Press. {{Taxonbar, from=Q5381979 Nautiloids