Cymatonota

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Synonyms: Chaenodomus Ulrich, 1894 (obj); Physetomya Ulrich, 1893; Endodesma Ulrich 1894; Psiloconcha Ulrich, 1894
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Pojeta, Jr. & Runnegar (1985):

• The orthonotid Cymatonota also has rugose comarginal ornament and a gaping shell.

Pojeta, Jr. (1971):

• For various reasons, several Ordovician genera have been considered to be burrowing forms including: Cymatonota, Psiloconcha, Orthodesma, Rhytimya, and Cuneamya.
• Of the genera listed above, Cymatonota is the best documented as an undoubted burrower. Nothing is known of the hinge or pallial line of this genus, and little is known of its musculature. However, it has a distinctly soleniform shape, with subparallel dorsal and ventral margins and it has both anterior and posterior gapes. In shell shape and gapes, Cymatonota is much like the later Paleozoic genera Palaeosolen, Prothyris, and Solenomorpha and should probably be allied to these forms. Cymatonota has traditionally been placed in the Modiomorphidae; however, its shell shape and gapes make it distinct from the byssate modioliform modiomorphids. Shells of the Cymatonota type seem to form a separate pelecypod lineage distinct from the Ordovician onward through the Paleozoic.
• Ordovician soleniform anomalodesmatans such as Cymatonota are interpreted as burrowing forms based on their elongate shell shape, subparallel dorsal and ventral margins, reduced umbos, and anterior and posterior shell gapes.

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

• Elongate, with subparallel dorsal and ventral margins; beaks about one-fourth distance from front end; ends rounded; umbonal ridge rounded; with broad lateral sulcus and commonly ventral sinus; surface essentially smooth, without radial ornamentation; posterior adductor larger than the anterior.

Ulrich (1893)

• Elongate solen-like shells, gaping more or less at both ends, with the hinge line long and extending in a straight line anterior and posterior to the small beaks; ventral and dorsal margins subparallel. Hinge plate very thin, edentulous; valves united by a delicate linear external ligament seemingly extending the full length of the hinge. Test very thin, marked externally with fine concentric lines, and on each side of the hinge line by short wave-like furrows. Pallial line and muscular scars so faintly marked that even in the best-preserved specimens they cannot be made out with certainty.

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