The figure below shows the distribution of samples containing the trilobite Triarthrus.

[ Triarthrus distribution ]

Triarthrus is a common trilobite in some parts of the MRV strata.

[ Triarthrus ] [ Triarthrus ]

Triarthrus Green, 1832 [*T. beckii ]
Exoskeleton elongate. Cephalon semicircular; glabella considerably wider than posterior areas of fixigenae, separated from front border by anterior border furrow or by short preglabellar field, with 2 to 4 pairs of lateral furrows, usually 1 or 2 anterior pairs separated from axial furrows; fixigenae very narrow, especially anterior and palpebral areas; anterior sections of facial sutures converging from eyes to front border; librigenae extremely narrow, spineless or (rarely) with slender, curved genal spines. Thorax of 13 to 16 segments, with axis wider than pleural regions, obliquely truncated or rounded pleural extremities, fulcrum placed very close to axis. Pygidium small, with 3 to 5 axial rings and entire, evenly rounded posterolateral margin.
Ord., North and South America, Europe
Family Olenidae Burmeister, 1843
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 varying greatly even in same subfamily; cephalic doublure and ventral sutures imperfectly known.
U. Cam. - U. Ord.
Order Ptychopariida Swinnerton, 1915

NOTE: The classification of trilobites has undergone several revisions since the 1959 publication of Volume O of the Treatise. The classification presented here only represents a starting point for the search for further information.

Treatise on Invertebrate Paleontology, O267