Early Ordovician – Late Ordovician
Cryptolithus is an extinct genus of fast-moving low-level epifaunal suspension feeders.
Identification in Hand Sample:
- Cephalon short and wide with long genal spines.
- Glabella inflated, either smooth, or with indistinct furrows.
- Generally lacks eyes.
- Thorax with 6 segments.
- The pygidium is short, wide, and rounded-subtriangular in outline.
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- Cryptolithus Green has an exoskeleton up to 3 cm in length. The cephalon is short, wide, semielliptical in outline, and has a wide fringe that is ornamented by concentric and radiating rows of pits; pleural areas are nearly twice as wide as the axis. The glabella is convex, expanding forward, and has three short pairs of lateral glabellar furrows. The occipital ring has a moderately long medial spine. Eyes are absent. Facial sutures are marginal. Pleural areas of fixigenae, inside fringe, are smooth and convex. Genal spines are long, narrow, and directed posteriorly. The thorax has 6 segments; pleural areas are wider than the axis; each pleaura is nearly straight and terminates bluntly. The pygidium is short, wide, and rounded-subtriangular in outline. The axis has several axial rings, and a terminal piece. Pleural fields have several pairs of shallow interpleural furrows.”
Shaw & Lesperance (1994):
- Museum and field restudy of Cryptolithus from all known geographic and stratigraphic occurrences in eastern North America shows that the principal variable character in this genus is the number of fringe pit arcs. Because this character varies within populations and even single individuals, it cannot be used to distinguish the earlier, typologically defined species of the genus. Instead, a neotype is designated here for the type species, Cryptolithus tessellatus Green, 1832, and morph designations are used for all pit arc variants. Over the timespan considered, the species increased the number of pit arcs, but the ecological and evolutionary mechanisms responsible cannot be identified with certainty.
Caster, Dalve & Pope (1961):
- The exclusively marine trilobites, related to the crabs, spiders, and insects, (Phylum, Arthropoda) abounded in the Paleozoic seas. They appear among the earliest well preserved fossils found in the Lower Cambrian (Waucobian), and continue into the Permian, although diminished in numbers after Devonian times. The Cincinnatian rocks are filled with trilobite fragments, and good specimens of the common genus, Flexicalymene, are abundant. Two other genera, Isotelus and Cryptolithus, somewhat rarer than Flexicalymene, and fragments of extremely rare genera, may be found here.
Green, J. (1832):
- “Among the numerous organic relics embedded in black limestone at Trenton Falls in the State of New York there is often found the fragment of a trilobite which cannot properly be referred to any of the genera already mentioned. Dr. J. Bigsby, in his Sketch of the Geology of the Island of Montreal, has figured and described a fossil which occurs at that place, which approaches in its specific characters to the fragments found at Trenton— but he does not suggest for his relic any name. Professor Brongniart has also represented, plate 4, figs. 5 and 7 A. B. C., the fragments of trilobites from Russia and from Llandillo, in Wales, which seem to differ but little from those above noticed these are also without names. Under such circumstances, we have thought it expedient to group these relics under the generic term of Cryptolithus, a name analogous to Calymene, Asaphus, Ogygia, and Agnostus, and which may with propriety be applied to the animal should it ever be discovered entire.
- Body contractile
- Buckler; lunate, convex, outer edge surrounded by a semicircular, reticulated or tessellated border
- Front or middle lobe of the buckler very protuberant
- Oculiferous protuberances, none
- Abdomen, much compressed.”