Strophomena nutans

Classification
Phylum: Brachiopoda
Class: Strophomenata
Order: Strophomenida
Family: Strophomenidae
Genus: Strophomena
Species: Strophomena nutans (Meek, 1873)

Taxonomic Details

Taxonomic History:

  • 1892 Strophomena nutans Hall and Clarke, Pal. New York, 8, pt. 1, p. 251, pl. 8, fig. 11; pl. 9 A, figs. 5-7; pl. 11 A, figs. 6, 7.
  • 1912 Stophomena nutans Foerste, Bull. Sci. Lab. Denison Univ., 17, p. 68, pl. 3, figs 2 A-E; pl. 9, fig. 15; pl. 10, figs. 2 A-C; pl. 11, fig. 8.

Stratigraphic Occurrences

S.nutans_strat

Geographic Occurrences

Map point data provided by iDigBio.

Stratigraphic Description

Sequences (Formations)

  • C5 Sequence (Waynesville)

Identification in Hand Sample

  • Small size, delicate striations, and thickened anterior margin
  • Small and deep muscle impression inside pedicle valve
  • Absence of fold and sulcus
  • A strongly concavo-convex species with pentagonal to sub-pentagonal outline
  • Posterior part of the brachial valve is flattened and shell is deflected strongly toward the anterior margin producing a subnasute appearance

Strophomena nutans from the Whitewater Formation of Maysville, Kentucky (OUIP 1951, first three) and the Waynesville Formation of Brookville, Indiana (OUIP 1589, far right)

Published Description

Davis (1998):

  • Articulate brachiopod. Differs from similar species by its small size, triangular outline, delicate striations, conspicuously thickened anterior margin, small and deep muscle impression inside pedicle valve, and absence of fold and sulcus. Waynesville.

McFarlan (1931):

  • A strongly concavo-convex, finely striated species of the S. planumbona type with pentagonal outline. Margins of posterior half of shell only moderately divergent. Hinge occasionally a little extended. On the pedicle valve and anterior part of the brachial (dorsal) valve several fine striae alternate with a coarse one, posteriorly on the brachial (dorsal) valve the striae are coarser and subequal or alternating in size. Anterior and lateral margins of pedicle valve abruptly and strongly thickened on the interior, the thickened border crossed by strong vascular markings. Width, 20-30 mm., length 0.7-0.8 width. Foerste (1912, p. 70) regards the typical form as the retarded gerontic form of S. concordensis.
  • Associated with S. neglecta and S. vetusta precursor forming a conspicuous Strophomena zone with a vertical range of only a few feet in the middle Blanchester from Lewis County, Kentucky to southern Indiana.

Foerste (1924):

  • Shell commonly narrower, but some same width as S. planumbona distinctly longer and usually more or less prolonged along the median line, so as to produce a nasute or sub-triangular outline; callous thickening along anterior margin of interior of the pedicle (ventral) valve broader and more conspicuous, especially along median parts of the valve, and here the vascular markings usually are more irregular. Although smaller, the valves usually are thick, suggesting gerontic characteristics, a feature also suggested by the more conspicuous callous thickening.
  • Locality and Horizon. Common in the Blanchester division, Waynesville member, Ohio and Indiana. A single but typical fragment in the Meaford, Clay cliffs (No. 8127).

Foerste (1912)

  • Strophomena nutans specimens represented by figures A, B, C, accompanying the original description, were 23 mm. wide and 21 mm. long. They have a sub-pentagonal outline. Anterior to a line drawn transversely across the center of the shell, the outline is broadly V-shaped, rounded at the anterior extremity. Posterior to this transverse line, the sides of the valve are only moderately divergent or nearly parallel. The posterior part of the brachial valve is flattened. From this flattened area, the shell is deflected strongly toward the anterior margin, especially toward the antero-lateral sides, producing a strongly voncex, subnasute appearance, which suggested the term nutans. The pedicel valve is rather strongly concave, the maximum depression being about two-thirds of the length of the shell from the beak. The radiating striae are fine, every fourth one tending to be slightly more prominent. The muscular area of the pedicel valve is deeply impressed, and the border of this area rises sharply and prominently above the general surface. The interior of the valve is conspicuously thickened along the border, the amount of this thickening being greatest near the middle of the anterior border, where it presents a very steep slope, having a height of almost 8 mm. above the general plane of the margin of the valve. This thickened border is crossed by strongly impressed grooves, called vascular markings, which are most conspicuous near the median parts of the border, where the latter attains the greatest elevation. Several ridges, limiting vascular grooves, extend posteriorly as far as the anterior border of the muscular area. The space between the muscular area and the thickened border is marked by small ovarian pits.