Phylum: Mollusca
Class: Bivalvia
Order: Arcoida
Family: Cyrtodontidae
Genus: Cyrtodontula Tomlin, 1931
Cincinnatian Species: Cyrtodontula umbonata

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Synonyms: (objective) Whitella Ulrich, 1890
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Geologic Range

Common Paleoecology
Cyrtodontula is an extinct genus of passively mobile semi-infaunal suspension feeders

Identification in Hand Sample:

  • Prominent beak
  • Strong umbonal ridge
  • Obliquely quadrangular or suboval
  • Swollen appearance of shell
  • 2 to 5 oblique folds or teeth in front of beak

Geographic Occurrences

Species Differentiation

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Fossils of Ohio (1996):

  • Strong umbonal ridge present
  • The Ordovician genus Cyrtodonula is represented by C. umbonata (Ulrich), which is medium sized and has prominent beaks and a truncate posterior margin.

Pojeta, Jr. (1971):

  • The Noetia-like shells are primarily a Late Ordovician development and are placed in the genus Cyrotdontula.
  • The Glycymeris-like cyrtodontids are placed in the genus Cyrtodonta and were probably shallow burrowers based on their general shell form. They may have burrowed like Cyrtodontula, leaving the posterior end of the shell sticking up out of the sediment; Glycymeris is known to adopt such a life position at times (Vlès, 1906).

Treatise on Invertebrate Paleontology, Part N, Mollusca 6(1 of 3) (1969):

  • Obliquely quadrangular or suboval, more or less ventricose; umbonal ridge and umbones prominent, escutcheon distinct; surface with fine concentric lines and random stronger concentric ridges; 2 to 5 rather oblique folds or teeth in front of beaks, a few posterior lateral teeth.

Soot-Ryen (1960):

  • Several internal casts can be referred to one or another of the genera of this family. Though no complete hinge could be studied, the ventricose form of the valves and the characteristic median keel indicate that some casts, at least, may belong to species of the genus Cyrtodontula Tomlin, 1931.

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C. umbonata