''Pentameroceras'' is a straight to slightly exogastric breviconic oncocerid from the middle

Silurian The Silurian ( ) is a geologic period and system spanning 23.5 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the third and shortest period of t ...

of North America and Europe belonging to the Trimeroceratidae. This

nautiloid Nautiloids are a group of cephalopods (Mollusca) which originated in the Late Cambrian and are represented today by the living ''Nautilus'' and ''Allonautilus''. Fossil nautiloids are diverse and species rich, with over 2,500 recorded species. Th ...

cephalopod A cephalopod is any member of the molluscan Taxonomic rank, class Cephalopoda (Greek language, Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral symm ...

produced a straight to slightly exogastric shell with a variable cross section that is generally circular, in which septa are close spaced and transverse, the body chamber is inflated. The aperture, which is constricted, consists of a narrow, vertical slit-like opening extending from the ventral hyponomic sinus to a dorsal sinus and two pairs of lateral sinuses that diverge in the upper portion.

Siphuncle The siphuncle is a strand of biological tissue, tissue passing longitudinally through the mollusc shell, shell of a cephalopod mollusc. Only cephalopods with chambered shells have siphuncles, such as the extinct ammonites and belemnites, and the li ...

s in the Trimeroceratidae are slender and empty.

References

* Sweet W.C. 1964. Nautiloidea-Oncocerida.

Treatise on Invertebrate Paleontology The ''Treatise on Invertebrate Paleontology,'' published from 1953–2007 by the Geological Society of America and the University of Kansas, then 2009–present by the University of Kansas Paleontological Institute, is a definitive multi-authore ...

, Part K. Geological Society of America and Univ. of Kansas press. Teichert & Moore, (eds)
Pentameroceras- Paleobio db
{{Taxonbar, from=Q7165021 Prehistoric nautiloid genera Oncocerida