- 1892 Orthis (Plectorthis) plicatella Hall, Hall & Clarke, p. 194, 221, pl. 5, figs. 18-20.
- 1932 Plectorthis plicatella (Hall) Schuchert & Cooper, p. 57, pl. 11, figs. 4,9.
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- C2 Sequence (Fairview: Fairmount)
Identification in Hand Sample
- Species with typically simple primary plications
- Larger specimens can attain a trace of secondary plications anteriorly
- Distinguished from similar species based on the distance from the beak at which secondary plications make their appearance and the relative prominence between primary/secondary plications
- Average width of an individual is around 20 mm but can attain a width up to 23 mm
Plectorthis plicatella from the Fairview Formation of Batavia, Ohio (OUIP 304)
- Articulate brachiopod. Fairmount.
- Discussion. This species is well characterized and widely distributed. Some degree of multiplication of the costae is typical. In the Minnesota specimens multiplication by bifurcation is limited to a small region close to the beak. Although newly formed costae originate at the level of the floor of the grooves and rise upward, thus giving the false appearance of implantation, they actually do branch from the side of an old costa.
- A species with typically simple primary plications though in the larger individuals there is usually a trace of secondary plications anteriorly. Width of average individual around 20 mm., length about 0.7 width. Fairmount of the Cincinnati region.
- In this species, the young specimens usually have simple primary plications only, and specimens of this character may occasionally attain a width of 20 to 23 mm. Usually, however, large specimens show at least a trace of secondary plications at a distance of about 9 to 10 mm. from the beak, although these may be still comparatively obscure 13 mm. from the beak. If this interpretation of the species be correct, Plectorthis equivalvis and Plectorthis fissicosta differ from Plectorthis plicatella chiefly in the distance from the beak at which the secondary plications make their appearance and in the relative prominence of the primary plications compared with the secondary ones.