Primaspis crosotus

Phylum: Arthropoda
Class: Trilobita
Order: Lichida
Family: Odontopleuridae
Genus: Primaspis
Species: Primaspis crosotus (Locke)

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Originally Ceraurus crosotus Locke
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Stratigraphic Occurrences


Geographic Occurrences

Map point data provided by iDigBio.
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Sequences (Formations)

  • C1 Sequence (Clays Ferry/Kope: McMicken, Southgate, Economy/Fulton)

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Identification in Hand Sample

  • Thoracic segments tapers into a spine.
  • Pygidium exhibits several sets of spines.
  • Fringed cephalic border and tuberculate surface-texture.
  • Spines of the shield and ribs nearly straight.

Primapsis crosotus from the Eden Formation of Cincinnati, Ohio (CMC 26215)

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Behrendt (2013):

  • Rarely exceeding 15 mm (.5 inch), this tiny trilobite is a spiny beauty. A member of Odontopleuridae, each of M. crosotus’ thoracic segments tapers into a spine. The pygidium also exhibits several sets of spines. Quite often, this trilobite is found within an indentation on bryozoa. And from this author’s experience, if one is found, there are usually others on the same matrix. Meadowtownella is found in the Kope Formation.

Hughes & Cooper (1999):

  • Locke’s Ceraurus crosotus (1843 b, c), a trilobite with a fringed cephalic border and tuberculate surface-texture, almost certainly should be placed in the genus Acidaspis Murchison, 1839. Locke’s drawing of his most-complete specimen is a rather fanciful rendering of a trilobite with a most un-Ceraurus-like, anteriorily tapering glabella. His subsequent drawings of pygidia of this tilobite (Locke, 1843c) may be that of Acidaspis or Primaspis. The pygidia of these two trilobites differ primarily in the number of pygidial spines; the spines are evidently broken in the specimens figured by Locke, and make positive identification of these specimens unlikely. Meek (1873a) provisionally placed Locke’s specimens in Acidaspis. Hughes and Cooper (1999) referred new specimens to Primaspis crosotus (Locke), presumably on the basis of cephalic characters, but the pygidial spines in the trilobites they illustrated were broken, rendering comparisons with Locke’s (1843b) specimens of C. crosotus moot.

Locke (1843):

  • The spines of the shield and of the several ribs are more nearly straight. Besides the spines terminating the ribs, there are six slender teeth, similar to those of the anterior fringe, attached, not to ribs, but to the terminal margin of the tail, four of them between the two last costal spines, at a, and the other two outside or anterior to the same, at b. Each of the costal arches is marked by two tubercules or “pimples”, one in the middle, and the other at the commencement of the free spine in which each costal arch terminates. These tubercles form four rows or lines down the body, two on each lateral lobe, the inner one being in the direction of the distant eyes.

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