Aspidopora eccentrica

Phylum: Bryozoa
Class: Stenolaemata
Order: Trepostomatida
Family: Monticuliporidae
Genus: Aspidopora
Species: Aspidopora eccentrica (James, 1882)

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Taxonomic History (Nickles & Bassler, 1900)

  • 1882 Monticulipora (Heterotrypa?) eccentrica James, Paleontologist, No. 6, p. 48; ibid., No. 7, pl. i, 6, 6a.
  • 1888 Monticulipora eccentrica James and James, Jour. Cincinnati Soc. Nat. Hist., X, p. 167, pl. ii, 2a-c.
  • 1893 Aspidopora eccentrica Ulric, Geol. Minnesota, III, p. 255.
  • 1894 Monticulipora eccentrica J.F. James, Jour. Cincinnati Soc. Nat. Hist., XVI, p. 185.

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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: Southgate)

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Identification in Hand Sample

  • Zoarium Morphology: Discoidal (5mm in diameter), Composed of 2 or more superimposed layers; Lower side concave, with wrinkled epitheca; characterized by the eccentricity of the concentrically wrinkled epitheca; smaller than E. newberryi: ~5mm in diameter
  • Zoecia: Circular to sub-elliptical
  • Mesozooids: Numerous, sometimes isolating the zooecia
  • Monticules: None – surface smooth
  • Maculae: Composed of larger apertures

Aspidopora eccentrica from the C5 Formation of Waynseville, Ohio (OUIP 1542)

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Holland (UGA Strat Lab 2013):

  • Small, free, disc, about 4 mm in diameter, with eccentric wrinkles on epitheca.

Bassler (1903):

  • Zoarium a small, free, subcircular expansion averaging 4 mm. in diameter and 1 mm. or less in thickness. Occasionally several of these disks may be found in contact and forming a zoarium as in A. areolata Ulrich. Celluliferous face smooth, slightly convex, and showing that the zoarium is composed of a single macula surrounded by zooecia of the normal size. Under surface flat or concave and lined with an epithecal membrane whose wrinkles or lines of growth are arranged about a point nearer the margin than the center of the base. Zooecial apertures rounded or ovate, the average diameter of the ordinary zooecium 0.3 mm. with 6 in 2 mm. while the largest zooecia of the maculae attain a diameter half again as great. Mesopores rather numerous, 6 usually surrounding a zooecium and occupying the interspaces left by the zooecia where their walls fail to touch. Acanthopores few and small and seldom detected either in section or on the specimens.
  • The internal characters of this form differ but little from other species of the genus. The large, elongate but few cystiphragms and the absence of diaphragms characterize the zooecial tubes while the mesopores are, as usual in this genus, closely tabulated.
  • This neat little species can readily be recognized by its small subcircular zoarium and eccentric wrinkles of the epithecated side. The species seems to be restricted to the middle division of the Eden shale in the Cincinnati area. Washings from certain shale beds will often yield hundreds of free samples while the limestone layers sometimes show an abundance of specimens on their surfaces. The best development of the species at Cincinnati occurs in the shales at the horizon 170 feet above low water mark in the Ohio River.

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