Numerous remains of Echinodermata occur in most sedimentary rocks, beginning with the Upper Cambrian rocks, and extending up to the recent period. The two orders Cystoidea and Blastoidea, which are the most lowly organised of the entire class, are exclusively Palaeozoic; and the Crinoidea are mostly referable to the same epoch. The more highly organised Asteroidea and Ophiuroidea commenced to be represented in the Silurian period; but the Echinoidea, with few exceptions, have no representatives earlier than the Carboniferous rocks. The following exhibits the geological distribution of the different orders of the Echinodermata in somewhat greater detail:
Crinoidea. The pedunculate Crinoidea attained their maximum in the Palaeozoic period, from which time they have gradually diminished down to the present day. On the other hand, the free Crinoids are comparatively modern, and seem to have reached their maximum at the present day. As has already been described, the Palaeozoic Crinoidea differ in some important particulars from those which succeeded them. The order is well represented in the Silurian, Devonian, and Carboniferous rocks, but especially in the latter; many Carboniferous limestones (crinoidal limestones and entrochal marbles) being almost entirely made up of the columns and separate joints of Crinoids. In the Secondary rocks Crinoids are still abundant. In the Trias the beautiful "Stone-lily" (Encrinus liliiformis) is peculiar to its middle division (Muschelkalk). In the Jurassic period occur many species of Apiocrinus (Pear-encrinite), Pentacrinus, and Extracrinus. The Chalk also abounds in Crinoids, amongst which is a remarkable unattached form (the Tortoise-encrinite or Marsupites).
Of the non-pediculate Crinoidea, which are a decided advance upon the' stalked forms, there are comparatively few traces; but remains of forms (such as Saccosoma and Solano-crinus) allied to the recent Comatulae have been found in the Jurassic and Cretaceous deposits.
Blastoidea. The Blastoidea, or Pentremites, are entirely Palaeozoic, and attain their maximum in the Carboniferous rocks, some beds of which in America are known as the Pen-tremite limestone, from the abundance of these organisms. They are, however, also found in the Silurian and Devonian rocks.
Cystoidea. These, like the preceding, are entirely Palaeozoic; but they are, as far as is yet known, almost exclusively confined to the Upper Cambrian and Silurian rocks, being especially characteristic of the horizon of the Bala limestone. The last known forms of Cystideans occur in the Devonian rocks. The oldest known Echinoderms are two extremely simple Cystideans (Trochocystites and Eocystites) which have been discovered in the primordial zone of North America.
Asteroidea. These have a very long range in time, extending from the Lower Silurian period up to the present day. In the Silurian rocks the genera Palaeaster, Stenaster, Palaeodiscus, and Petraster are among the more important, the greater number of forms being Upper Silurian. The next period in which Star-fishes more especially abound is the Oolitic (Mesozoic); the more important genera being Uraster, Luidia, Astropecten, Plumaster, and Goniaster, some of which have survived to the present day. Many Star-fishes occur, also, in the Cretaceous rocks, the genera Oreaster, Goniodiscus, and Astrogonium being among the more noticeable. In the Tertiary rocks few Star-fishes are known to occur, but Goniaster and Astropecten are represented in the London Clay (Eocene).