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Weeksina unispina (Walcott, 1916)
Characteristics of this trilobite are the backward directed spine on the 8th of 10 segment of the articulated middle part of the body (or thorax), and the second pair of furrows from the back on the raised central part of the headshield (or cephalon) called glabella, which curve from inward to fully backward, almost isolating a pair of lobes, just in front of the occipital ring, that is defined by a furrow that crosses the entire width of the glabella. Weeksina is known only from the Weeks Formation at North Canyon, House Range, Millard County, Utah.
Weeks Upper Middle Cambrian, Cenomanian Stage USAywang21
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Modocia whiteleyi (Robison & Babcock, 2011)
Diagnosis Modocia having a short (sagittal) preglabellar field, narrow palpebral areas, short genal spines, 12 thoracic segments with angular terminations, moderate-sized pygidium with distinct medial notch, and 4 rings in the pygidial axis. Etymology After Thomas E. Whiteley, for promoting knowledge of trilobites (Whiteley, Kloc, and Brett, 2002). Discussion Modocia whiteleyi differs from all other species of Modocia by having only 12 thoracic segments. It further differs from most Modocia by its short preglabellar field and narrow palpebral areas. Specimens of this species are illustrated commonly on the Internet as either Modocia hewlisca or M. weeksensis, both of which are taxonomically invalid names (nomina nuda).
Weeks Upper Middle Cambrian, Cenomanian Stage USAywang21
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Norwoodia boninoi (Robison & Babcock, 2011)
Diagnosis Norwoodia with wide anterior and lateral cephalic border furrow. Glabella short, slightly tapered, diminishing in relative length through ontogeny; lateral furrows weak to effaced. Occipital furrow weak to effaced. Occipital ring, with medial node, merging rearward into long, stout, variably flattened occipital spine. Palpebral lobes about half as long as glabella, opposite anterior glabella. Anterior sections of facial suture weakly divergent, posterior sections diverge laterally and slightly forward to border furrow and then gently curve rearward to lateral cephalic margin. Genal spines long and stout, similar in length to occipital spine, all three approximately reaching an imaginary transverse line near thoracic-pygidial boundary. Cephalic doublure with small anterior rostellum and posterior median suture. Thorax containing nine segments; unusually narrow and subcircular in outline, being slightly more than half as wide as maximum width of cephalon. Fourth thoracic segment having exceptionally long, slender, posteriorly directed, medial spine, its length greater than exoskeleton without spine. Pygidium tiny, short, and alate; width more than three times length; axis with two rings. Etymology After Enrico Bonino, for promoting knowledge of trilobites. Discussion Norwoodia boninoi is a macrocephalic trilobite that has a general morphology reminiscent of, and probably convergent with, some mid-Paleozoic bellinurid xiphosurans.
Weeks Upper Middle Cambrian, Cenomanian Stage USAywang21
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Meniscopsia beebei (Robinson & Babcock 2011)
Diagnosis Exoskeleton ovate with low relief and somewhat variable width. Cephalon crescent shaped. Lateral cephalic borders widen rearward into stout, broad-based genal spines. Anterior sections of facial suture moderately divergent, posterior sections strongly divergent. Glabella unfurrowed, long, slightly tapered, bluntly rounded anteriorly, reaching anterior border furrow. Occipital ring short. Palpebral lobes slightly posterior to glabellar midpoint. Hypostome conterminant, with front margin broadly abutting laterally wide and sagittally narrow rostral plate along hypostomal suture. Thorax containing 10 sagittally short, weakly falcate segments. Pygidium large, semicircular, with broad, smooth border that widens rearward.Pygidial axis tapering to rounded terminus, length about 0.6 times that of pygidium; containing eight weakly defined rings and terminal piece. Pleural fields of pygidium triangular and very weakly furrowed. Exoskeletal doublure significantly widens rearward beneath cephalon, showing slight abrupt increase beneath posterior cephalic border, then similar width beneath thorax, further slight broadening beneath pygidium, and slight medial constriction behind axial terminus. Etymology After Matthew A. Beebe, for unpublished contributions (1990) to knowledge of the Weeks Formation and its fauna. Revision for publication of work on the Weeks Formation by Beebe ended with his untimely death in 1994. Discussion During holaspid ontogeny, the pygidium of Meniscopsia beebei increased disproportionately in size relative to the cephalon. For example, the pygidium of a paratype, 15 mm in length (Fig. 29.4), is slightly shorter than the cephalon in sagittal length, whereas the pygidium of the holotype, 33 mm in length (Fig. 29.1), is almost 1.5 times longer than the cephalon in sagittal length. Variation in late holaspid exoskeletal width may be related to differences in postmortem compression. Internal anatomy of trilobites is rarely preserved.This Meniscopsia beebei show a dark central feature that can be interpreted to be an early diagenetic filling of the alimentary tract and paired laterally projecting digestive glands (foregut and midgut glands), with one pair per segment, as in some modern chelicerate arthropods.
Weeks Upper Middle Cambrian, Cenomanian Stage USAywang21
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Lonchocephalus plena (Walcott 1916)
Lonchocephalus plena is an extremely rare and diminutive ptychopariid trilobite collected from the Weeks Formation in the House Range, Millard County, Utah
Weeks Upper Middle Cambrian, Cenomanian Stage USAywang21
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Genevievella granulata (Walcott, 1916)
Genevievella is a genus of trilobites with a short inverted egg-shaped outline, a wide headshield, small eyes, and long genal spines. The backrim of the headshield is inflated and overhangs the first of the 9 thorax segments. The 8th thorax segment from the front bears a backward directed spine that reaches beyond the back end of the exoskeleton. It has an almost oval tailshield with 5 pairs of pleural furrows. It lived during the Upper Cambrian in what are today Canada and the United States.
Weeks Upper Middle Cambrian, Cenomanian Stage USAywang21
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Deiracephalus aster (Walcott, 1916)
Species of Deiracephalus Resser, 1935, are rare elements in most Guzhangian (upper Marjuman) trilobite faunas of Laurentian North America, and are characterized by striking cephalic spinosity that includes very long genal and occipital or preoccipital glabellar spines. Almost all previous reports of the genus have assigned sclerites to two species, Deiracephalus aster (Walcott, 1916) and Deiracephalus unicornis Palmer, 1962. They usually range up to at least 20mm in length, has a large occipital spine and a medial spine of siilar size on each of 10 thoracic segements. Large, outwardly and backwardly directed genal spines are unusual in arsing from just inside the cephalic border rather than from the outer border surface, as in most polymerid trilobites.
Weeks Upper Middle Cambrian, Cenomanian Stage USAywang21
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Cedarina schachti n. sp.
Diagnosis Frontal area and preglabellar field long; anterior border evenly anteriorly arcuate; anterior sections of facial suture strongly anteriorly divergent; palpebral lobes large; pygidium relatively narrow and long. Etymology The species is named in honour of Robert Schacht, who collected and donated the holotype and one of the paratype specimens. source: The Marjuman trilobite Cedarina Lochman: thoracic morphology, systematics, and new species from western Utah and eastern Nevada, USA The thorax of C. schachti has ten segments. The segments have a simple morphology (Fig. 5), featuring a well impressed pleural furrow with a transverse course and distal pleural regions that are tapered into blunt, posteriorly directed pleural spines. The eighth segment bears a long median axial spine. None of the other segments bear any axial nodes or spines. This morphology is all but identical to that seen in the articulated "richardsonellines" cited above. The only difference is that the remopleuridids have two additional thoracic segments posterior to the spine-bearing eighth.
Weeks Upper Middle Cambrian, Cenomanian Stage USAywang21
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Cedaria minor (Walcott, 1916)
This trilobite is a member of the family Cedariidae known as Cedaria minor. Cedaria is a small, rather flat trilobite with an oval outline, a headshield and tail shield of approximately the same size, 7 articulating segments in the middle part of the body and spines at the back edges of the head shield that reach halflength of the body. Cedaria lived during the early part of the Upper Cambrian (Dresbachian), and is especially abundant in the Weeks Formation.
Weeks Upper Middle Cambrian, Cenomanian Stage USAywang21
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Beckwithia typa (Resser, 1931)
This specimen is a rare example of the aglaspid Beckwithia. Aglaspids resemble the modern-day horseshoe crabs, and contain as the most famous member the Beckwithia typa shown here, a monsterous creature reaching up to some 20 cm in overall length that is thought to have Beckwithia was named after Frank Beckwith, editor and publisher of the Millard County Chronicle of Delta, Utah in the early to middle 1900s, a man with a passion for trilobites. Aglaspids are thought by some scientists to have made the The aglaspidids survived into the Early Ordovician but died out by the end of the period. It has been proposed that they are related to the ancestors of horseshoe crabs and arachnids.
Weeks Upper Middle Cambrian, Cenomanian Stage USAywang21