Phylum: Brachiopoda
Class: Lingulata
Order: Lingulida
Family: Trematidae
Genus: Trematis Sharpe, 1848
Cincinnatian Species: Trematis millepunctata

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Geologic Range
Upper Ordovician

Common Paleoecology
Trematis is an extinct genus of stationary, low-level, epifaunal suspension feeders.

Identification in Hand Sample:

  • Biconvex shell
  • Circular to suboval shape
  • Rounded to rectangular superficial pits variably arranged on the shell
  • Subcentral apex of ventral valve
  • Margins of pedicle notch straight or concave toward the midline
  • Pedicle opening large and elongated
  • Low dorsal median ridge
  • Two bean-shaped, composite muscle scars on interior of dorsal valve

Geographic Occurrences

Map point data provided by iDigBio.
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Treatise on Invertebrate Paleontology, Part H, Vol. 2 (2000):

  • Shell dorsibiconvex, circular to suboval; ornament of small, rounded to rectangular, superficial pits variably arranged, commonly in rough quincunx or in rows radiating from beak; ventral valve with subcentral apex, margins of pedicle notch straight or concave toward midline; dorsal pseudointerarea not raised above valve floor; dorsal median ridge low, variably developed, separating two bean-shaped composite muscle scars

Fossils of Ohio (1996):

  • A medium-sized acrotretid brachiopod that has a biconvex profile and a circular outline. The pedicle valve has a large, elongate pedicle opening that extends to the valve margin. Small pits are characteristic on the surface of both valves. This genus is known from the Cincinnatian Series

Caster, Dalve & Pope (1961):

  • The inarticulate brachiopods are distinguished from the articulate forms by the absence of a hinge, a different musculature, and shells of calcium phosphate-chitin rather than calcium carbonate. In the Cincinnatian these may be frequently seen as thin, oval shells adhering to larger brachiopod shells (Petrocrania, Schizocrania), as chalky shells with minute punctae (pores) in the valves (Trematis) or as glossy, triangular shells (“Lingula”). Since the inarticulates appear in the Cambrian before the articulates, they are considered the evolutionary precursor of the articulates.

New York State Museum Annual Report of the Regents (1892):

  • Shell sub-circular or transversely oval in outline. Pedicle-valve unevenly convex, more or less depressed over the posterior region; apex at, or behind the center; directly beneath it begins the pedicle-fissure, which transects the shell, vertically widening to posterior margin with straight or outwardly curving edges. Brachial valve evenly convex, with its apex marginal and slightly projecting. On the interior, the pedicle-valve shows a faint median furrow extending from the angle of the fissure to the apex of the shell; this groove widens at its apical termination and may represent a point of muscular attachment. The sides of the fissure are often thickened by callosities similar to those sometimes seen in species of Orbiculoidea. From the apex of the valve extend radiating and branching vascular sinuses.
    In the brachial valve, the posterior margin is much thickened and broadly grooved to allow the extrusion of the pedicle. This thickening does not take the form of a cardinal area or shelf, but is rather a callosity appressed against the interior surface of the shell, the central portion being projected beyond the margin of the pedicle-valve. Directly below and in front of this area re two transversely elongate scars, adjustors or posterior adductors, which are usually partly concealed by the progressive overgrowth of the cardinal thickening. A faint median septum begins between these scars and passes forward, becoming more prominent over the tongue-shaped median elevation which separates the large central scars. These impressions are oblique and are not simple, each appearing to be composed of two, if not three distinct scars, making a posterior, a median and an anterior pair. What appears to be the posterior pair is small, and sometimes quite sharply defined, the central pair very much larger, and the nterior pair narrow, situated at either side of the angle of the median callosity and separated by its apex. The specialization of the first of these scars is not satisfactorily established; the entire impression is deeply excavated. In some well-preserved specimens, there is also evidence of external, marginal scars lying just in front of the outer ends of the posterior adductors.
    Surface of both valves more or less completely covered by beautiful ornamentation consisting of punctures or small pittings of various depth, arranged in either quincunx or in radiating rows; in the later case they may be distant from one another without intervening ridges, or lie in radiating furrows, when they are either circular or subrectangular.
    Shell-substance composted of an outer calcareous layer with a series of inner corneous lamellae. The outer layer varies in thickness in different species, and is coarsely punctated by the pittings constituting the surface ornamentation. The corneous layersare impunctate.

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T. millepunctata