Originally : Orthis fissicosta (Hall) , also referred to as Plectorthis dichotoma by some authors.
Map point data provided by iDigBio.
- C2 Sequence (Fairview: Mount Hope, Fairmount)
- Cardinal line somewhat less than the width of the shell
- Foramen narrow, triangular, and reaching to the apex
- Dorsal valve moderately convex, with the beak extending and slightly incurved
- Surface marked by angular costse, which become bifid and trifid on the center or toward the margin of the shell
- Costae number between 19 and 20
Plectorthis fissicosta from Mt. Hope formation of Clermont County, Ohio(MUIP 11599)
- Articulate brachiopod. Differs from preceeding species in larger maximum size, more numerous plications, splitting of plications, and slight sulcus and fold.
“Semi-oval, with the cardinal line somewhat less than the width of the shell; area narrow ; foramen narrow, triangular, reaching to the apex ; dorsal valve moderately convex, with the beak extending and slightly incurved; ventral valve moderately convex in the middle and depressed at the sides ; surface marked by angular costse, which become bifid and trifid on the center or toward the margin of the shell; number of costae about 19 or 20. Found at Cincinnati, from 300 to 400 feet above low water-mark,though Prof. Hall obtained, as he says, “but a single specimen near Cincinnati, showing that the shell is comparatively rare,” yet it would not be extraordinary for a collector to pick up a hundred specimens in a day, at an elevation of about 340 feet, back of Cincinnati. It is found at Hamilton, Butler county, near Lawrenceburg, Indiana, and in Warren and Clermont counties, showing that it is persistent in its range, which is probably confined between 300 and 500 feet above low water. It is rather more abundant than its associate, O. plicatella, from which it may readily be distinguished by its divided costse.”