Phylum: Arthropoda
Class: Trilobita
Order: Ptychopariida
Family: Olenidae (Burmeister, 1843)
Cincinnatian Genera: Triarthrus

Geologic Range
Late Cambrian – Late Ordovician

Common Paleoecology
Olenidae is an extinct family of fast-moving, low-level, epifaunal carnivores.

Description of the Family

  • Subovate to elongate trilobite.
  • Cephalon has narrow, threadlike, prominent border.
  • Usually has distinctly defined eye ridges with small to medium sized eyes.
  • 9 to 19 thoracic segments, and 3 to 7 axial rings in pygidium.
  • Other characteristics highly variable, even in same subfamily.
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Treatise on Invertebrate Paleontology, Part O, Vol. 1 (1959):

  • Exoskeleton opisthoparian, subovate to elongate, usually small, micropygous to heteropygous. Cephalon usually with narrow threadlike, prominent border, usually distinctly defined eye ridges, and eyes of small to medium size. Thoracic segments 9 to 19, with furrowed pleurae. Pygidium with 3 to 7 axial rings, pleural fields distinctly segmented. Hypostoma probably free. Other characters greatly varying even in same subfamily; cephalic doublure and ventral sutures imperfectly known.

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