resilium

from The Century Dictionary.

• noun In the pelecypod mollusks, an internal part of the ligament, lamellar in structure and composed of horny fibers, with a considerable intermixture of lime which may aggregate and form an accessory shelly plate (ossiculum or lithodesma). The resilium acts as a plug against which the valves, when closed, are brought into opposition, and its tendency therefore is to push the valves asunder.