Shell is broad with dorsal valve concave, ventral valve convex, straight hinge line with ears, ornamented with concentric growth lines, radiating lines and spines, ventral valve with two hubs on either side of a central sulks (depression) that runs from the umbo to anterior margin. Age – Carboniferous to Permian.
Spirifer:
Shell is broad, triangular, and biconvex with straight and long hinge line with ears and cardinal area. The surface is ornamented we radial ribs, anterior margin dentate, dorsal valve with ridge and ventral valve with sulks. Age- Silurian to Permian.
Rhynchonella:
ADVERTISEMENTS:
Shell triangular, hinge line curved, umbo small and curved, anterior margin produced into a tongue like projection, surface ornamented with strong ribs. Age – Upper Jurassic.
Terebratula:
Shell biconvex, elongated, egg shaped, and large ventral umbo with pedicle opening, curved hinge line, anterior margin of both the valves with two folds, ornamented with fine concentric growth lines. Age – Late Mesozoic to Late Tertiary.