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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.]

A suborder of Crinoidea found chiefly in the Paleozoic rocks.

A genus of extinct Paleozoic brachiopods, often very abundant in the Upper Silurian. Pentamerus limestone (Geol.), a Silurian limestone composed largely of the shells of Pentamerus.

n, next following the Carboniferous, and regarded as closing the Carboniferous age and Paleozoic era. -- n.

including numerous species, many of them of large size. They are characteristic of the Paleozoic formations. The radiating septs, when present, are usually in multiples of four. See Cyathophylloid.

t. of Bird. -- Secondary rocks or strata (Geol.), those lying between the Primary, or Paleozoic, and Tertiary (see Primary rocks, under Primary); -- later restricted to strata of the Mesozoic age, and at but little used. -- Secondary syphilis (Med.), the second stage of syphilis, including the period from the first d…

aining to the country of the ancient Silures; -- a term applied to the earliest of the Paleozoic eras, and also to the strata of the era, because most plainly developed in that country.

Any one of numerous species of small, conical fossil shells found in Paleozoic rocks. They are supposed to be pteropods.

ry common in the Silurian and Devonian periods, but became extinct at the close of the Paleozoic. So named from the three lobes usually seen on each segment.

An extinct genus of cyathophylloid corals common in the Paleozoic formations. It is cup-shaped with numerous septa, and with a deep pit in one side of the cup.