This elegant crinoid is found all round our coasts, and its range extends from Norway to the shores of the Mediterranean. In swimming, the movements of its arms exactly resemble the alternating stroke given by the medusa to the liquid element, and have the same effect, causing the animal to raise itself from the bottom and to advance back foremost, even more rapidly than the medusa. When dying, either in fresh water or in spirits, it emits a most beautiful purple colour, which tinges the liquid in which it is killed. The _Ophiuridæ_, or _snake-stars_, are essentially distinguished from the true _star-fishes_ by the long serpent or worm-like arms, which are appended to their round, depressed, urchin-like bodies. They have no true suckers with which to walk, their progression being effected (and with great facility) by the twisting or wriggling of their arms, which are moreover in many species furnished with spines on the sides, assisting locomotion over a flat surface. These arms are very different from those of the true star-fishes, which are lobes of the animal's body, whereas the arms of the Ophiuridæ are mere processes attached or superadded to the body. These animals are very generally distributed through the seas of our earth, both of its northern and southern hemispheres, but are found largest in the tropical ocean. In our own waters they are very abundant, and are among the most curious and beautiful game pursued by the dredger. [Illustration: Sand-star.] The British Ophiuridæ belong to two generic types, that of the _Ophiuræ_ and that of the _Euryales_. The former, to which the sand and brittle-stars belong, have simple arms; the latter, arms ramifying into many processes.