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

[ Cryptolithus distribution

Cryptolithus is a common trilobite in a few parts of the MRV strata.

Cryptolithus Green, 1832 [*C. tesselatus]
Fringe with concentric rows of pits that show radial arrangement also anteriorly, characteristically with raised radial ridges between outer row or rows and concentric ridge between inner rows, one row of pits external to girder.
L. Ord. - U. Ord., North America, British Isles
Family Trinucleidae Hawle & Corda, 1847
Cephalic fringe broad, sloping outward, bilaminar, with numerous pits on external surfaces, extending posterolaterally somewhat behind rest of cephalon; convex occipital ring commonly with backward-directed spine, occipital furrow with deep apodemal pit; glabella expanding forward, reaching to inner margin of fringe, deep anterior pits at extremities of axial furrows; genae subtriangular in outline, with or without eye tubercles and faint eye ridges; lower lamellae of fringe bearing genal spines. Thorax with 6 segments; convex axial rings, with deep apodemal pits in articulating furrows; pleurae with broad diagonal pleural furrows, pleural tips bent down. Pygidium triangular, length 0.25 to 0.5 of width; axis with many rings; pleural fields with shallow pleural furrows. Surface of glabella and genae may bear reticulate pattern of raised ridges, margin of fringe and pygidial border with terraced lines.
L. Ord. - 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, O422.