Modiolopsis modiolaris

Phylum: Mollusca
Class: Bivalvia
Order: Modiomorphida
Genus: Modiolopsis
Species: Modiolopsis modiolaris (Conrad, 1838)

Stratigraphic Occurrences

M. modiolaris_strat

Geographic Occurrences

Map point data provided by iDigBio.

Stratigraphic Description

Sequences (Formations)

  • C2 Sequence (Fairview: Fairmount)

Identification in Hand Sample

  • Distinct, comparatively straight hinge line posterior to the beak
  • Basal margin moderately convex to nearly straight
  • Median sulcus absent
  • Conspicuous extension of the anterior margin of the shell in front of the beak

Modiolopsis modiolaris from McMillan formation of Boone County, Kentucky(OUIP 984)

Published Description

Davis (1998):

  • Pelecypod. Internal mold. Genus found throughout Cincinnatian; this species is restricted to Fairmount

Pojeta, Jr (1971):

  • Fortunately Conrad’s holotype of Modiolopsis modiolaris has been preserved (fide Hall 1847, p 295 and Ulrich 1924 p 32 explanation) and it is figured herein on plate 15 figures 1-3. It is a composite mold of a distinctly modioliform shell with anisomyarian musculature and concentric sculpture. The museum label accompanying the holotype gives the locality as “Pulaski beds Late Ordovician Rome, N.Y.” this differs somewhat from the locality as given by Conrad 1838. In general form and musculature, M. modiolaris is distinctly mytilacean. Nothing definite is known about the dentition of this species although Ulrich 1924 regarded Modiodesma type species. Modiolopsis modiolaris as being edentulous. Specimens similar to M. modiolaris from the Pulaski Shale of New York and elsewhere show that the species has multiple accessory muscle scars anterior to the beaks (probably anterior pedal byssal retractors) pl 16 figs 1 2 an integropalliate pallial line (pl. 16 figs 1-2) and an elongate opisthodetic ligament (pl 15 figs 5-6). The ligament is only rarely preserved and then only as a dark stain connecting the two valves.

Foerste (1924):

  • Ventral margin forming angle of 10 to 17 degrees with hinge-line; moderately convex or nearly straight, never intercurved. Anterior margin and lower posterior margin rather rapidly rounded; posterior margin forming an angle of about 130 to 135 degrees with hinge-line, curving strongly toward front on approaching the latter. Valves relatively flat. Beaks low and closely appressed, located a considerable distance back from the anterior margin. Umbonal parts rather strongly flattened, but not depressed into a mesial sinus. Surface, with concentric striae more distinctly developed anteriorly than along posterior margin.
  • Locality and Horizon. Originally described from the Pulaski member of the Lorraine formation, near Pulaski, New York. Specimen figured by Hall in the Paleontology of New York, on Plate 81, as figure 1 a is from the same horizon, Rome, New York.

McFarlan (1931):

  • The principal features are the comparatively straight hinge line posterior to the beak, a moderately convex or nearly straight basal margin, absence of median sulcus, and conspicuous extension of the anterior margin of the shell in front of the beaks. The umbonal ridge disappears ventrally in the general convexity of the shell. Measurements after figures by Foerste (1914b, p. 282) are: length about 60 mm., height at beak about 1/3 length, height posteriorly about ½ length, beaks 10-11 mm. behind anterior margin; convexity of valve about 4 mm., angle between cardinal and ventral margin 11-12 degrees. Maysville and Richmond.