Trilobites of the Weeks Formation


House Range, Millard County, Utah


Ammagnostus beltensis

Arapahoia sp.

Aspidagnostus sp.

Beckwithia typa (Resser, 1931)

Beckwithia sp.

Blountia sp.

Cedaria minor (Walcott, 1916)

[Cedaria sp.] = "Gerospina schachti"

Chiasmacantha cecrops

Coosella sp. type 1

Coosella sp. type 2

[Democephalus granulatus] = "Genevievella" granulatus (Walcott, 1916)

[Densonella semele (Walcott, 1916)] = Menomonia semele (Walcott, 1916)

[Densonella n. sp.] = Menomonia n. sp.

Dresbachia amata Walcott, 1916

Dresbachia sp.

"Genevievella" granulatus (Walcott, 1916) - old name was Democephalus granulatus

"Gerospina schachti" Shanan Peters dissertation, 2003, unpubl.) - old name was Cedaria sp.

Lejopyge acantha Robison, 1964 = L. multifora Opik, 1979

Lejopyge calva Robison, 1964

Lejopyge  multifora Opik, 1979

Lonchocephalus plena

Maryvillia arion

Menomonia calymenoides 

Menomonia semele (Walcott, 1916) - old name was Densonella semele (Walcott, 1916)

Menomonia n. sp. [=Densonella n. sp.]

Meteoraspis dis

[Modocia hewlisca] = "Modocia weeksensis"

Modecia hewlisca (type 1)

Modecia hewlisca (type 2)

Modecia hewlisca (type 3)

Also see: "Modocia weeksensis" (Shanan Peters dissertation, 2003, unpubl.) - old name was Modocia hewlisca

"Nephalicephalus beebei" (Shanan Peters dissertation, 2003, unpubl.)

Norwoodia bellaspina (Shanan Peters dissertation, 2003, unpubl.)

Norwoodella sp.




Schachtenella ultraspinus

Selenocoryphe platura (Shanan Peters dissertation, 2003, unpubl.)

Selenocoryphe sp.

Triadaspis bigeneris

[Tricrepicephalus coria (Walcott, 1916)] = Tricrepicephalus texanus (Shumard, 1861) (see Pratt, 1992)

Tricrepicephalus texanus (Shumard, 1861) - old name was Tricrepicephalus coria

Tricrepicephalus n. sp.

Weeksina unispina (Walcott, 1916)


undescribed trilobite

Weeks layers absent trilobites sometimes produce soft-bodies trilobite relatives sensu Hou & Bergström (Hou & Bergström, 1997: Arthropods of the Lower Cambrian Chengjiang fauna, southwest China. Fossils & Strata, Number 45, 22nd December 1997, pp. 1-116). These Trilobitamorphs include aglaspids and lamellipeds.


The Weeks Formation trilobites are currently under investigation, and many of the trilobites will be formally published in the near future (by Dr. Shanan Peters). Most of the trilobites in this faunal list are from: Shanan Peters dissertation, 2003; Beebe's 1990 unplublished thesis; and from Bob Schacht (pers. comm.). Some of the species listed above may be invalid, or may be synonomous with other species. Many of the genera have not as yet been formally recognized. Some species are still under controversy (for example: the Tricrepicephalus species referred to as T. coria, have been synonomized with T. texanus (see Pratt, 1992, Peters, 2003), although this is not as yet universally accepted. The jury is still out until more specimens of Tricrepicephalus are found.Many thanks to Shanan Peters and Bob Schacht for their invaluble help assembling the Weeks faunal list!



    The following 3 plates are from Dr. Shanan Peters' unpublished dissertation, 2003:

Plate 1 (includes: Cedaria minor, Weeksina unispina,and Gerospina schachti)

Plate 2 (includes: Menomonia semele, Dresbachia amata, Nephalicephalus beebei, Selenocoryphe platyura, Norwoodia bellaspina, and Modocia weeksensis)

Plate 3 (includes: Genevievella granulatus, Tricrepicephalus texanus, Beckwithia typa, and Lingulella sp.

Some Acknowledgements:

Many thanks to Dr. Shanan Peters for his permission to use these unpublished plates (Shanan Peters, unpubl. dissertation, 2003). As these are unpublished plates, and the sole property of Dr. Peters, permission from the author must be gained in order to reproduce these plates. Please note that these plates are not from the final, peer-reviewed version of the manuscript.

Shanan E. Peters
University of Michigan
Museum of Paleontology
1109 Geddes Road
Ann Arbor, MI 48109-1063

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