''Lonchodomas'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

trilobite Trilobites (; meaning "three lobes") are extinct marine arthropods that form the class Trilobita. Trilobites form one of the earliest-known groups of arthropods. The first appearance of trilobites in the fossil record defines the base of the At ...

s, that lived during the Ordovician. It was eyeless, like all raphiophorids, and had a long straight sword-like frontal spine, that gradually transforms into the relatively long

glabella The glabella, in humans, is the area of skin between the eyebrows and above the nose. The term also refers to the underlying bone that is slightly depressed, and joins the two brow ridges. It is a cephalometric landmark that is just superior to ...

. Both the glabellar spine and the backward directed genal spines are subquadrate in section. ''Lonchodomas'' has five thorax segments and the pleural area of the pygidium has two narrow furrows. ''Lonchodomas'' occurred in what are today

Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...

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A.V. Krylov (2003).
New data on trilobites from Hecker mud mounds (Ordovician) in the Leningrad region (in Russian)
. ''Vestnik Sankt-Petersburgskogo Universiteta, Seriya Geologiya i Geografiya'' 3(33):95-96) and the

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Distribution

* ''L. carinatus'' is found in the Upper Ordovician of the United States (Lower Member and Botetourt limestone Member, of the Edinburgh Formation, Shenandoah County, Virginia, 39.0° N, 78.4° W Blackriveran 460.9 - 449.5 Ma) * ''L. clavulus'' is present in the Middle Ordovician of Newfoundland, Canada ('' Histiodella kristinae'' conodont zone, Table Cove Formation; Table Point, "Middle Table Head" and Table Cove). * ''L. mcgeheei'' is present in the Upper Ordovician of Oklahoma, United States (

Bromide Formation The Bromide Formation is a geological formation in Oklahoma, USA. It is well known for its diverse echinoderm and trilobite fossil fauna. Location The Bromide Formation crops out in the Arbuckle and Wichita Mountains and in the Criner Hills ...

, Sandbian). * ''L. retrolatus'' was collected from the Ordovician of Nevada (Eureka Quartzite, sandy limestone, 60–90 ft above base, Ranger Mountains, Nevada Test Site)) * ''L. rostratus'' is known from the Upper Ordovician of Estonia (Narva open pit, and Lasnamägi, Kukruse Stage, Sandbian) and Latvia (Remte 3 borehole, and Adze 6 borehole, Kukruse Stage,

Sandbian The Sandbian is the first stage of the Upper Ordovician. It follows the Darriwilian and is succeeded by the Katian. Its lower boundary is defined as the first appearance datum of the graptolite species '' Nemagraptus gracilis'' around million yea ...

). * ''L. suriensis'' was excavated from the Middle Ordovician of Argentina (Portillo del Cajón, Cerro Morado; Cerro Suri; Puesto El Despacho; Las Pircas; all La Rioja) * ''L. volborthi'' occurs in the Lower Ordovician of the Russian Federation (Volkhovian level, Syas River, Putilovo and Babino quarries, St.Petersburg region). It was originally described as ''Ampyx volborthi'' but assigned to ''Lonchodomas'' in 1952 by Steinar Skjeseth.Steinar Skjeseth, 1952.
On the lower Didymograptus zone (3B) at Ringsaker, and contemporaneous deposits in Scandinavian
: ''Norsk geol. tidsskr''., v. 30, p. 138 — 182.

Description

Like all raphiophorids, ''Lonchodomas'' is eyeless. The headshield (or

cephalon Cephalon, Inc. was an American biopharmaceutical company co-founded in 1987 by pharmacologist Frank Baldino, Jr., neuroscientist Michael Lewis, and organic chemist James C. Kauer—all three former scientists with the DuPont Company. Baldino s ...

) and tailshield (or pygidium) are subtriangular in outline. ''Lonchodomas'' looks a lot like

Ampyx In Greek mythology, Ampyx (Ancient Greek: Ἄμπυξ) or Ampycus (Ἄμπυκος ''Ampykos'' means 'woman's diadem, frontlet') was the name of the following figures: * Ampyx, also called Ampycus or AmpyceHesiod, ''Shield of Heracles'' 180 was a ...

but the glabella is diamond-shaped in outline, and it has a ridge along the midline (it is carinate). The glabella gradually transforms into the spine, which makes it difficult to determine where the spine begins. The long median glabellar spine is subquadrate in section and is directed horizontally forward, from the frontal tip of the glabella. The glabella has 2 pairs of muscle scars. The genal spines are also subquadrate in section. The thorax has 5 segments. The pleural regions of pygidium have 2 pairs of narrow pleural furrows.

References

{{Taxonbar, from=Q6669670 Raphiophoridae Asaphida genera Ordovician trilobites Fossils of Argentina Fossils of Estonia Fossils of Latvia Fossils of Norway Fossils of Russia Fossils of the United States Bromide Formation Paleozoic life of Newfoundland and Labrador Paleozoic life of the Northwest Territories Paleozoic life of Quebec Paleozoic life of Yukon