The fauna of the Silurian System bears in all its three great types the stamp of a fashion peculiarly antique, and which, save in a few of the mollusca, has long since become obsolete. Its radiate animals are chiefly corals, simple or compound, whose inhabitants may have somewhat resembled the sea-anemones; with zoophites, akin mayhap to the sea-pens, though the relationship must have been a remote one; and numerous crinoids, or stone lilies, some of which consisted of but a sculptured calyx without petals, while others threw off a series of long, flexible arms, that divided and subdivided like the branches of a tree, and were thickly fringed by hair-like fibres. There is great variety and beauty among these Silurian crinoids; and, from the ornate sculpture of their groined and ribbed _capitals_ and slender _columns_, the Gothic architect might borrow not a few striking ideas. [Illustration: Fig. 46. CYATHAXONIA DALMANI.] The difference between the older and newer fashions, as exemplified in the cup-shaped corals, may be indicated in a single sentence. The ancient corals were stars of four rays, or of multiples of four; the modern corals are stars of six rays, or of multiples of six. But though, at a certain definite period,--that during which the great Palæozoic division ended and the Secondary division began--nature, in forming this class of creatures, discarded the number four, and adopted instead the number six, the great leading idea of the star itself was equally retained in corals of the modern as in those of the more ancient type. [Illustration: Fig. 47. GLYPTOCRINUS DECADACTYLUS. (Hudson River Group, Lower Silurian.)] [Illustration: Fig. 48. CALYMENE BLUMENBACHII.] [Illustration: Fig. 49. ORTHISINA VERNEUILI.] [Illustration: Fig. 50. LITUITES CORNU-ARIETIS.] [Illustration: Fig. 51. LINGULA LOWISII.]