Early Ordovician – Middle Silurian
Heterorthidae is an extinct genus of stationary epifaunal suspension feeders.
Description of the Family
- Large, transversely semioval to subquadrate.
- Flabellate diductor muscle scar.
- Dorsal interior usually with lobate, commonly modified cardinal process.
- Fulcra plates absent.
Treatise on Invertebrate Paleontology, Part H, Vol. 3 (2000):
- Normally transversely semioval to subquadrate, large, rectimarginate dalmanelloids with aditicules variably developed; ventral interior with extended, flabellate diductor muscle scar, anterior ends commonly widely splayed, not enclosing adductor scar; dorsal interior usually with lobate, commonly modified cardinal process, brachiophores as thickened rods, lacking plates; fulcra plates absent; dorsal mantle canal system normally lemniscates, ventral system probably lemniscate.
Boucot et al.(1965):
- Diagnosis. Concavo-convex to unequally bi-convex rhipidomellids having the greater convexity in the pedicle valve, in which the muscle field is large and commonly flabellate with scalloped anterior margins that may or may not enclose the medial adductors. The family includes Heterorthis Hall & Clarke, 1892, Diceromyonia Wang, 1949, and Svobodaina Havlicek, 1953.
- Discussion. In its outline, short hinge line, broad flabellate diductor impressions enclosing the adductors, and lack of fulcral plates.