The figure below shows the distribution of samples containing the trilobite Isotelus.
Isotelus is a common trilobite in some parts of the MRV strata.
- Isotelus DeKay, 1824 [*I. gigas ]
- Cephalon and pygidium mostly with poorly defined flattened border. Frontal area moderately long, cephalic axis ill-defined, almost obsolete in several species, slightly expanding in front of medium-size eyes situated somewhat behind transverse mid-line of cranidium; no posterior border furrow; genal angles rounded, pointed, or with short genal spines. Hypostoma almost parallel-sided, posterior margin with broad, deep notch; anterior lobe short. Thoracic axis considerably broader than pleurae. Pygidial axis broad, poorly defined, almost obsolete in several species; pleural fields smooth or very faintly ribbed.
M. Ord. - U. Ord., North America, Siberia, Northern Europe, Greenland
- Family Asaphidae Burmeister, 1843
- Librigenae separated anteriorly by a median suture; glabella well defined to obsolete, considerably longer than frontal area; lateral glabellar furrows mostly weak or absent; most genera with distinct glabellar tubercle; eyes generally somewhat distant from axial furrows; faint, almost obsolete eye ridges known only in 2 genera. Doublure commonly broad; posterior margin of hypostoma varying from pointed to deeply notched. Thorax of 8 segments; pleural furrows generally diagonal, if present. Panderian organs developed as notches or separate openings, but absent in some (Ogygiocaridinae, Symphysurininae). External margin of pygidium varying from rounded to pointed, in some genera with terminal spine; paired pygidial spines present only in single genus of uncertain affinities. Dorsal surface of carapace with small pits, terrace lines, or both; no tuberculate or granulose ornamentation. Family tends toward loss of apparent segmentation of cephalon and pygidium, obsolescence of axial furrows, and deep notching of posterior margin of hypostoma.
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, O339.