What is an extinct order of sea urchins found in the Paleozoic rocks. They had more than twenty vertical rows of plates. Called also Palæechini. [Written also Palæechinoidea.] called?

paleechinoidea — An extinct order of sea urchins found in the Paleozoic rocks. They had more than twenty vertical rows of plates. Called also Palæechini. [Written also Palæechinoidea.]. (Webster's 1913.)

Sources