Gravicalymene Shirley, 1936, is a genus of trilobites belonging to the order Phacopida, suborder Calymenina and family Calymenidae. Species included in this genus have previously been allocated to Calymene Brongniart 1822,Flexicalymene Shirley, 1936. and Sthenarocalymene Siveter 1977.
Aspidaeglina is an extinct genus from a well-known class of fossil marine arthropods, the trilobites. It lived during the early part of the Arenig stage of the Ordovician Period, a faunal stage which lasted from approximately 473 to 470 million years ago.
Marrellomorpha are an extinct group of arthropods known from the Cambrian to the Early Devonian. They lacked mineralised hard parts, so are only known from areas of exceptional preservation, limiting their fossil distribution. The best known member is Marrella, with thousands of specimens found in the Cambrian aged Burgess Shale of Canada. The group is divided up into two major orders, Marrellida and Acercostraca. Marrellida is recognised by the possession of head shields with two or three pairs of elongate spine-like projections, and three pairs of uniramous appendages on the cephalon, while Acercostraca generally have large ovoid carapaces that cover the entire upper half of the body, and five pairs of uniramous cephalic appendages. Both groups have unbranched antennules and a segmented trunk with biramous appendages. Recent research has suggested the previously enigmatic Cambrian trilobite-like arthropods Skania and Primicaris belong to this group. Their phylogenetic position is uncertain, various studies have alternatively placed them in the Arachnomorpha as relatives of Artiopoda, as related to Mandibulata, or as stem group euarthropods. Some authors have proposed that they may be closely related to sea spiders (Pycnogonida) within Chelicerata though the cladistical support for such a relationship is relatively weak.
Gilwern Hill is a hill about 3 mi / 5 km southeast of Llandrindod Wells in the county of Powys, Wales.
For the Skiddaw group of hills, see Skiddaw Group
Trinodus is a very small to small blind trilobite, a well known group of extinct marine arthropods, which lived during the Ordovician, in what are now the Yukon Territories, Virginia, Italy, Czech Republic, Poland, Denmark, Sweden, Svalbard, Ireland, Scotland, Wales, Iran, Kazakhstan and China. It is one of the last of the Agnostida order to survive.
Sphaeragnostus is an extinct genus from a well-known class of fossil marine arthropods, the trilobites. It can be recognized by having two thorax segments, a totally effaced headshield, while the tailshield although effaced, has a clear furrow parallel to its border, and a short, convex, subcircular axis. It lived during the Ordovician.
Ogygiocarella Brongniart, 1822, is a genus of asaphid trilobites. It occurred during the Middle Ordovician.
Geragnostus is a genus of very small agnostid trilobites whose fossils are found Ordovician-aged marine strata from Eurasia, North America and Argentina.
Cyclopyge is a genus of small to average size trilobites that lived during the Ordovician. Like all members of the family Cyclopigidae, it has very large convex eyes, that cover most of the free cheeks, and in some species touch each other. The eyes almost touch the large glabella. The occipital ring has merged with the rest of the glabella. The glabella does not extend into a frontal thorn. The cephalon lacks genal spines. The 6 thorax segments have short pleurae. The pygidium is rather large, and often rather effaced. These are features that also occur in other Cyclopygidae, and are indications of a pelagic lifestyle.
Symphysops is a genus of trilobites of average size, belonging to the Cyclopygidae family. It had a cosmopolitan distribution and lived from the Middle to the Upper Ordovician. It has been found in Canada, China, the Czech Republic (Bohemia), Iran, Ireland, Kazakhstan, Poland, Morocco, Spain, Scotland and Wales. The name Symphysops refers to the fused eyes, common to the species of this genus. Some (sub)species of the cyclopygid genera Cyclopyge and Pricyclopyge share this character, but Symphysops uniquely combines the merged eye with a frontal thorn on the head and the "lower eyelid".
Prospectatrix is a genus of trilobites of average size, that lived in the Lower Ordovician and is probably ancestral to the other genera of the Cyclopygidae family. Its eyes are only moderately enlarged and it has six or seven thorax segments.
Cyclopygidae is a family of asaphid trilobites from the Ordovician. Cyclopygids had an extratropical distribution, and there is evidence that they lived in darker parts of the water column. Cyclopygids are characterized by enlarged eyes, with a wide angle of view, both horizontal and vertical, reminiscent of the eyes of dragonflies. These typically touch the glabella directly on the side. Cyclopygids all lack genal spines, but Symphysops carries a forward directed frontal spine on the glabella. It is presumed that at least the members of the genus Pricyclopyge swam upside down and had bioluminescent organs on the third thorax segment. Cyclopygids had between 7 and 5 thorax segments, a wide and stout axis, and short side lobes.
Sagavia is a genus of trilobites that lived during the Middle and Upper Ordovician in what are now Northwest and Southeast China, North Kazakhstan and Wales. It is a typical cyclopygid that can be distinguished by its large but separate eyes, elongated glabella, five thorax segments and a pygidium with clearly defined axis and border.
Pricyclopyge is a genus of trilobites assigned to the family Cyclopygidae that occurs throughout the Ordovician. Pricyclopyge had an extratropical distribution, and there is evidence that it lived in darker parts of the water column. Pricyclopyge has huge eyes, an inverted pear-shaped glabella, six thorax segments, with on the 3rd two small discs. Pricyclopyge is known from what are today China, the Czech Republic, France, and the United Kingdom.
Cnemidopyge is a genus of trilobites that lived during the Ordovician. Like all Raphiophorids it is blind, with a cephalon that is subtriangular to subsemicircular, carrying genal spines and a forward directed rapier-like spine on the central raised area, with the front of the glabella inflated and the natural fracture lines of the cephalon coinciding with its margin. It may be easily distinguished from other raphiophorids by the rectangular thorax with 6 segments, where other genera have a different number of segments and segments change in width over the length of the thorax. Uniquely in this genus, the inner pleural region of the frontal segment is enlarged. Also the axis and pleural fields of the pygidium are strongly segmented.
Telephinidae is a family of pelagic trilobites with large wide-angle eyes, occupying most of the free cheeks, downward directed facial spines and 9-10 thorax segments. The family is known during the entire Ordovician and occurred in deep water around the globe.
The Letná Formation is a Late Ordovician geologic formation of the Prague Basin, Bohemian Massif in the Czech Republic. The formation crops out in the Czech capital, more specifically at Letná Hill, after which the formation is named. The type locality is located at Malá Strana, Holešovice district.
Aponileus is an extinct genus of trilobites. Chung-Hung Hu circumscribed the genus in 1963. The genus was once considered a junior subjective synonym of the genus Psephosthenaspis but it is considered to be a distinct genus again. As of 2021, fossils have been found in Greenland, Texas, and Utah. They all date to the Upper Floian (Blackhillsian) within the Ordovician Period.
Dudleyaspis is an extinct genus of Lower to Middle Devonian odontopleurid trilobites that lived in a shallow sea that lay between Euramerica and Gondwana. It was named in 1949 by Prantl & Pribyl.
