The pebbles went ploop and sunk to the bottom of the pond.

Whalers have always overexploited their stocks, driving them to commercial extinction. […] American whalers, operating at first from the coast and later in sea-going boats, took about 200 000 right whales in addition to humpbacks and grays.

This specimen shows a wide, concave and smooth fossula with a clear-cut thread tying the first tooth to the first denticle; there are still four other irregular denticles after which the inside part of the fossula sinks and roundens.

You will find the term defined at the end of Roman one.