Zygospira modesta

Phylum: Brachiopoda
Class: Rhynchonellata
Order: Atrypida
Family: Anazygidae
Genus: Zygospira
Species: Zygospira modesta (Say)

Taxonomic Details

Taxonomic History:

  • 1847 Atrypa modesta Hall, Pal. New York, 1, p. 141, pl. 15, fig. 15.
  • 1893 Zygospira modesta Hall and Clarke, Pal. New York, 8, pt. 2, p. 155, figs. 146-149; pl. 54, figs. 7-10, 12.
  • 1910 Zygospira modesta Foerste, Bull. Sci. Lab. Denison Univ., 16, p. 29, pl. 2, figs. 15 A, B.
  • 1924 Zygospira modesta Foerste, Upper Ordovician faunas in Ontario and Quebec, p. 127-128, pl. 10, fig. 21 a, b.

Stratigraphic Occurrences


Geographic Occurrences

Map point data provided by iDigBio.

Stratigraphic Description

Sequences (Formations)

  • C6 sequence (Elkhorn, Whitewater)
  • C5 sequence (Whitwater, Liberty, Waynesville)
  • C4 sequence (Arnheim)
  • C3 sequence (Mount Auburn, Corryville, Bellvue)
  • C2 sequence (Fairview: Fairmount, Mount Hope)
  • C1 sequence (Clays Ferry/Kope: McMicken, Southgate, Economy/Fulton)

Identification in Hand Sample

  • Tiny in size (9 mm wide, 8 long and 4 thick)
  • Fold in ventral valve and sulcus in dorsal
  • 4 plications in sulcus, 7-9 on slopes on each side (around 18 total per valve)
  • Central plication strongest
  • Plano-convex with an extended beak; prominent and incurved
  • The pedicle foramen is depressed convex
  • Pedicle foramen nearly circular to broadly oval
  • Obscurely punctate surface

Zygospira modesta from Waynesville formation of Warren County, Ohio (OUIP 1488)

Published Description

Holland (UGA Strat Lab, 2013)

  • Usually 7-9 primary lateral plications on either side of fold.

Fossils of Ohio (1996):

  • Articulate brachiopod. Entire Cincinnatian. (the less common Z. cincinatiensis is larger, pentagonal in shape, and has fewer plications; it occurs in the upper Kope and the Fairview)

Foerste (1924):

  • Type specimen 7.8 mm long, 9.2 mm wide and 4.1 mm thick. Pedicle (ventral) valve has eighteen distinct plications, and two indistinct ones, the latter being near the hinge-margin. The four median plications, moderately elevated above the general convexity of shell and forming a low, median elevation. Groove along median line of elevation wider than the two adjacent grooves. Corresponding to the median groove, brachial (dorsal) valve has a comparatively strong median plication; the two adjacent plications, one on each side, are narrower. A broad, but shallow depression extends from near the beak to the anterior margin of the shell; lateral borders not sharply defined , but formed approximately by the third plication on each side of the median plication. Characterized by low, median fold, and many lateral plications, all primary. IN the type there are seven of these on each side, but many have eight and even nine. Some specimens are 10 mm long.
  • Large specimens of Zygospira have been figured recently by Raymond from the Collingwood shale at Cragleith, Ontario. For these the term Z. raymondi here is suggested, regarding it as a new species. In the Nicolet River section, this species attains a length of 11 mm, and a width of 14 mm. It differs from typical Z. kentuckiensis in being less distinctly flattened along median part of pedicle (ventral) valve, and, therefore, in being less angular on the lateral margins of this flattened area, where the lateral slope of the valve starts downward (No. 8513).
  • Locality and Horizon. Described from the Cincinnatian formation at Cincinnati, Ohio, where the typical specimens occur in the Fairmount, but it appears to range from the lower Eden to the upper Richmond. Abundant in the Waynesville member of Quebec.

McFarlan (1898):

  • A small species. Width, 9 mm., length, 8 mm., thickness 4 mm., with low median fold on the pedicle valve and sinus on the brachial. The sinus is occupied by about four plications and 7-9 occur on each lateral slope. The median groove on the fold of the pedicle valve is distinctly wider than the adjoining grooves and in the sinus the corresponding plication is comparatively stronger.

Geological and Natural History Survey of Minnesota (1885):

  • Suborbicular or plano-convex with the beak extended. Width a little greater than the length; cardinal lie distinctly marked and somewhat extended; dorsal [ventral] valve convex, with an elevated ridge along the center, occupied by four plaits which are stronger than the others; beak prominent, incurved and perforated, the perforation [pedicle opening] valve depressed-convex, broadly oval or nearly circular, with a broad but ill defined sinus along the middle, the central plication stronger than the others, with a smaller one on each side; each valve with about eighteen simple, rounded plications, surface obscurely punctate.