Amongst the _Echinodermata_, all those orders which have hard parts capable of ready preservation are more or less largely represented. We have no trace of the Holothurians or Sea-cucumbers; but this is not surprising, as the record of the past is throughout almost silent as to the former existence of these soft-bodied creatures, the scattered plates and spicules in their skin offering a very uncertain chance of preservation in the fossil condition. The Sea-urchins (_Echinoids_) are said to be represented by examples of the old genus _Paloechinus_. The Star-fishes (_Asteroids_) and the Brittle-stars (_Ophiuroids_) are, comparatively speaking, largely represented; the former by species of _Palasterina_ (fig. 60), _Paloeaster_ (fig. 60), _Paloeocoma_ (fig. 60), _Petraster, Glyptaster_, and _Lepidaster_--and the latter by species of _Protaster_ (fig. 61), _Paloeodiscus, Acroura_, and _Eucladia_. The singular _Cystideans_, or "Globe Crinoids," with their globular or ovate, tesselated bodies (fig. 46, A, C, D,), are also not uncommon in the Upper Silurian; and if they do not become finally extinct here, they certainly survive the close of this period by but a very brief time. By far the most important, however, of the Upper Silurian Echinodenns, are the Sea-lilies or _Crinoids_. The limestones of this period are often largely composed of the fragmentary columns and detached plates of these creatures, and some of them (such as the Wenlock Limestone of Dudley) have yielded perhaps the most exquisitely-preserved examples of this group with which we are as yet acquainted. However varied in their forms, these beautiful organisms consist of a globular, ovate, or pear-shaped body (the "calyx"), supported upon a longer or shorter jointed stem (or "column"). The body is covered externally with an armour of closely-fitting calcareous plates (fig. 62), and its upper surface is protected by similar but smaller plates more loosely connected by a leathery integument. From the upper surface of the body, round its margin, springs a series of longer or shorter flexible processes, composed of innumerable calcareous joints or pieces, movably united with one another. The arms are typically five in number; but they generally subdivide at least once, sometimes twice, and they are furnished with similar but more slender lateral branches or "pinnules," thus giving rise to a crown of delicate feathery plumes. The "column" is the stem by which the animal is attached permanently to the bottom of the sea; and it is composed of numerous separate plates, so jointed together that whilst the amount of movement between any two pieces must be very limited, the entire column acquires more or less flexibility, allowing the organism as a whole to wave backwards and forwards on its stalk. Into the exquisite _minutioe_ of structure by which the innumerable parts entering into the composition of a single Crinoid are adapted for their proper purposes in