File:Flexicalymene meeki (fossil trilobite) (Cincinnatian Series, Upper Ordovician; Cincinnati area, USA) 15.jpg

English: Flexicalymene meeki (Foerste, 1910) - fossil trilobite (pygidium & posterior thorax) from the Ordovician of the Cincinnati area, USA. (fossil is ~1.5 centimeters across at its widest)

Trilobites are extinct marine arthropods. They first appear in Lower Cambrian rocks and the entire group went extinct at the end of the Permian. Trilobites had a calcitic exoskeleton and nonmineralizing parts underneath (legs, gills, gut, etc.). The calcite skeleton is most commonly preserved in the fossil record, although soft-part preservation is known in some trilobites (Ex: Burgess Shale and Hunsruck Slate). Trilobites had a head (cephalon), a body of many segments (thorax), and a tail (pygidium). Molts and carcasses usually fell apart quickly - most trilobite fossils are isolated parts of the head (cranidium and free cheeks), individual thoracic segments, or isolated pygidia. The name "trilobite" was introduced in 1771 by Johann Ernst Immanuel Walch and refers to the tripartite division of the trilobite body - it has a central axial lobe that runs longitudinally from the head to the tail, plus two side lobes (pleural lobes).

Classification: Animalia, Arthropoda, Trilobita, Polymerida, Calymenidae

Stratigraphy: unrecorded/undisclosed Upper Ordovician unit (but likely from the Flat Run Trilobite Lagerstätte, mid-Arnheim Formation, lower Richmondian Stage, upper Upper Ordovician)

Locality: unrecorded/undisclosed (but likely from the Flat Run Trilobite Quarry, far-southwestern Highland County, southwestern Ohio, USA)