Early Ordovician (Arenig) – Early Silurian (Llandovery)
Dalmanella is an extinct genus of stationary epifaunal suspension feeders
Identification in Hand Sample:
- Has a gently biconvex profile, and the oval to subcircular outline is truncated by a straight hinge line
- The brachial valve has a shallow sulcus
- Ribs radiate from the beaks toward the commissure
- Ventral interior with dental fossettes, cordate muscle scar, and divergent dental plates
- Note that the common species formerly known as D. multisecta and D. meeki are now placed in the new genus Cincinnetina.
- All three species listed below likely belong to Heterorthina, according to Dr. Jisuo Jin, who is currently studying these species. Heterorthina can be recognized based on the presence of a dorsal medial groove or medial interspace (as opposed to a medial rib) and a prominently trilobate cardinal process. These species have not yet been formally assiged to Heterorthina.
Fossils of Ohio (1996):
- Dalmanella is a small to medium-sized orthid brachiopod. It has a genly biconvex profile, and the oval to subcircular outline is truncated by a straight hinge line. Width is greater than length, although it may be just so. The brachial valve has a shallow sulcus. Ribs radiate from the beaks toward the commissure. The ribbing may be finer than that of Plaesiomys and Glyptorthis and is certainly finer than that of Plectorthis. Species of Dalmanella have been referred to as Onniella by some workers (for ex. Walker, 1982) Dalmanella had been recorded from much of the Cincinnatian Series.
Treatise on Invertebrate Paleontology, Part H, Vol. 3 (2000)::
- Subcircular, variably biconvex to ventribiconvex valves; ventral interior with dental fossettes, cordate muscle scar, and divergent dental plates; dorsal interior with brachiophores plates convergent onto median ridge; fulcra plates normally present.
Williams and Wright (1963):
- Unequally biconvex, coarsely to finely costellate shells with the brachial valve less convex and variably sulcate; ventral muscle field cordate, sub-median diductor lobes usually extending beyond adductor; brachiophores with their bases convergent onto the median ridge, fulcral plates usually present; undifferentiated bilobed cardinal process, dorsal adductor scar quadripartite, elongately suboval; ventral vascula media slightly divergent.
- Shells plano-convex or subequally biconvex. Pedicle-valve usually the deeper, often gibbous, elevated at the umbo and arched over the cardinal area. Hinge-line generally shorter than the greatest width of the shell. In many of the species there is a more or less conspicuous, undefined median fold and sinus on the pedicle and brachial valves respectively. Surface covered with fine, round bifurcating striae.
- In the pedicle-valve the teeth are quite prominent, thickened at their extremities and supported by lamellae which are produced forward circumscribing a rather short suboval or subquadrate muscular area, which is more or less indistinctly defined in different species and in different conditions of the shell.
- In the brachial valve the the cardinal process extends forward as a median ridge separating the muscular impressions. The inner surface of this process is divided by a faint median furrow which produces two lobes at the posterior extremity, and each of these lobes is again divided, making the process quadrilobate. Sometimes the inner divisions of the two main lobes have coalesced, producing a strong median lobe and thus making the process appear trilobate. The dental sockets are small, the crural plates often greatly elevated, especially in the plano-convex forms, and they are not usually produced into a ridge about the muscular area, but end abruptly. Muscular impressions quadruplicate, sometimes with radiating ridges extending from the lateral and anterior margins.