Ischyrodonta elongata

Phylum: Mollusca
Class: Bivalvia
Order: Modiomorphida
Family: Allodesmatidae
Genus: Ischyrodonta
Species: Ischyrodonta elongata Ulrich, 1890

Taxonomic Details

  • 1890 Ischyrodonta elongata Ulrich, Amer. Geol., 6, p. 175, figs. 12a-c.
  • 1893 Ischyrodonta elongata Ulrich, Geol. Surv. Ohio, 7, p. 675, pl. 54, figs. 20-21
  • 1908 Ischyrodonta elongata Cumings, 32nd Ann. Rep. Dep. Geol. Nat. Res. Indiana, p. 1000, pl. 45, figs. 4, 4a.

Stratigraphic Occurrences


Geographic Occurrences

Map point data provided by iDigBio.

Stratigraphic Description

Sequences (Formations)

  • C6 Sequence (Elkhorn)
  • C5 Sequence (Lower Whitewater, Waynesville)

Identification in Hand Sample

  • Shell is large and elongate
  • Strongly convex
  • Prominent, compressed beaks
  • Deep anterior muscle scar
  • Anterior end is rounded and very short

Ischyrodonta elongata from the Waynesville Formation of Waynesville, Ohio (OUIP 1821)

Published Description

Fossils of Ohio (1996):

  • Isochyrodonta is represented by I. elongata Ulrich, which is medium sized, narrowly elongate species having a distinct anterior muscle scar evident on internal molds

Cumings (1907):

  • “Of this species only casts of the interior have been seen. These may be described briefly as follows: Shell rather large transversely elongate-ovate, widest posteriorly, strongly convex with point of greatest convexity a little in front of the middle. Beaks prominent, compressed, almost terminal. Cardinal margin convex; posterior margin rather strongly convex; posterior margin rather strongly convex, and generally somewhat straightened in the lower half; basal margin straight or faintly sinuate; anterior end abruptly rounded, very short. Anterior muscular scar deep, subquadrate, situated beneath the beaks. Just above it the small accessory scar.”
  • “The much greater length of this shell distinguishes it from I. truncata with which it is associated. The outline is much like Modiolopsis modiolaris Conr., but the casts of that species are not so convex and the beaks are less prominent.” – Ulrich

Ulrich (1893):

  • Shell large for the genus, transversely elongate-ovate, widest posteriorly, strongly convex, with point of greatest convexity a little in front of the center. Beaks rather large, compressed, almost terminal; unbonal ridge rather strong, mesial sulcus broad. Cardinal margin strongly arcuate; posterior margin nearly vertical in the middle and lower part, uniformly rounded above, sharply curved at the base; ventral margin faintly and broadly sinuate; anterior end very short and abruptly rounded. Surface marked with strong and irregular lines of growth.In casts of the interior the beaks are very prominent, incurved, and greatly compressed by the deep umbonal sulcus, behind which the somewhat curved and sharply elevated umbonal ridge is distinguishable almost to the basal line. Anterior muscular scar deep, subrhomboidal, sharply defined on the upper side, radially marked and situated immediately beneath the beak. Just above it is the small pedal muscle scar. Posterior scan faint, ovate; pallial line distinct in the basal part of the valves.
  • This fine species, though closely related to I. truncate, is readily distinguished by its much greater length. The next species is also related but is smaller and widely different in the post-cardinal part of its outline.
  • Formation and Locality. – Near the top of the Cincinnati group, at Oxford, Ohio, and Richmond, Indiana.