All the ordinary joints of the arms are provided with muscles producing various motions, and binding the joints firmly together. If one of the arms get entangled, or fall into the jaws or claws of an enemy, by a jerk the star-fish can at once get rid of the embarrassed arm; and as all this group have a wonderful power of reproducing lost parts, the arm is soon restored. Unfortunately, most of the examples of Pentacrinus asteria hitherto procured have had the soft parts destroyed and the disk more or less injured. One specimen, however, in my possession is quite perfect. The body is covered above by a membrane closely tessellated with irregularly formed flat plates. The mouth is a rounded opening of considerable size in the centre of the disk, and opens into a stomach passing into a short curved intestine which ends in a long excretory tube--the so-called “proboscis” of the fossil crinoids--which rises from the surface of the disk near the mouth. From the mouth five deep grooves, bordered on either side by small square plates, run out to the edge of the disk, and are continuous with the grooves on the upper surface of the arms and pinnules, while in the angles between them five thickened masses of the mailing of the disk surround the mouth like valves. These were at first supposed to answer the purpose of teeth. The crinoids, however, are not predatory animals. Their nutrition is effected in a very gentle manner. The grooves of the pinnules and arms are richly ciliated. The crinoid expands its arms like the petals of a full-blown flower, and a current of sea-water bearing organic matter in solution and suspension is carried by the cilia along the brachial and radial grooves to the mouth. In the stomach and intestine the water is exhausted of assimilable matter, and the length and direction of the excretory proboscis prevent the exhausted water from returning at once into the ciliated passages. Two other fixed crinoids were dredged from the _Porcupine_, and these must be referred to the Apiocrinidæ, which differ from all other sections of the order in the structure of the upper part of the stem. The Apiocrinidæ attained their maximum during the Jurassic period, when they were represented by many fine species of the genera Apiocrinus and Millericrinus. The chalk genus Bourguetticrinus shows many symptoms of degeneracy. Rhizocrinus loffotensis, M. Sars, was discovered in the year 1864, at a depth of about 300 fathoms, off the Lofoten Islands, by G. O. Sars, a son of the celebrated Professor of Natural History in the University of Christiania, by whom it was described in the year 1868. It is obviously a form of the Apiocrinidæ still more degraded than Bourguetticrinus, which it closely resembles.