Solenopsidae.-Shell equivalve, greatly elongated, umbones very far forward.
The young Brachiopod in all its species is protected by an embryonic shell called the " protegulum," which sometimes persists in the umbones of the adult shells but is more usually worn off.
In the entire animal the posterior end projects slightly more than the anterior from the region of the umbones.
a, b, right and left valves of the shell; c, d, the umbones or short arms of the lever; e, f, the long arms of the lever; g, the hinge; h, the ligament; i, the adductor muscle.
Hinge pliodont, that is to say, it has numerous teeth on either side of the umbones and the teeth are perpendicular to the edge.