59:3.11

Toward the close of the final Silurian submergence there is a great increase in the echinoderms—the stone lilies—as is evidenced by the crinoid limestone deposits. The trilobites have nearly disappeared, and the mollusks continue monarchs of the seas; coral-reef formation increases greatly. During this age, in the more favorable locations the primitive water scorpions first evolve. Soon thereafter, and suddenly, the true scorpions—actual air breathers—make their appearance.