The numerous fossilized remains of these curious creations, which abound in different rocks, attracted the attention of learned men at an early period. The encrinites were among the earliest objects of scientific description. As early as the sixteenth century, the celebrated mineralogist, George Agricola, mentions them under the names of _Entrochites_, _Trochites_, and _Astroïtes_. At the same time, and since that epoch, the Crinoïdæ, which we know by the name of stone-lilies, and which characterises the _Muschelkalk_ rocks, have been known under the name of Encrinus, from εν, stone, and κρίνον, a lily. [Illustration: Fig. 107. Pentacrinus caput Medusæ (Müller).] During the eighteenth century the works upon the Crinoïdæ were very numerous, though not very correct. They sometimes reported these organic remains to be vegetable; sometimes they were beings allied to the star-fishes; at others they were the vertebral column of fishes. Towards the year 1761, however, Guettard, one of the most learned naturalists of his time, understood the real nature of these productions. He had occasion to examine a recent Encrinus sent from Martinique under the name of _Sea-Palm_, which was in reality _Pentacrinus caput Medusæ_. The comparison of the living individual with the fossil fragment described by his predecessors, and of which he had specimens in his collections, enabled him to ascertain the real origin of the fossil Encrinoidæ. The beautiful fragment which still exists in the Museum of Natural History at Paris was long considered unique, but it is now known that ten others exist in different museums. Since that date the Crinoïdæ have been examined and described by observers such as Miller, Forbes, D'Orbigny, and Pictet, and very elaborately by Major Austin. [Illustration: Fig. 108. Pentacrinus Europæus (Thompson).] "The species of fixed Crinoïdæ actually living are _Pentacrinus caput_ _Medusæ_ (Fig. 107), and _Pentacrinus Europæus_ (Fig. 108). These curious zoophytes resemble a flower borne upon a stem, which terminates in an organ called the calyx, but which is, properly speaking, the head of the animal. Arms, more or less branching, spring from this calyx, their ramifications, so formed, consisting of many pieces articulated to each other. The calyx is supported by a stem, varying in height, formed of pieces secreted by the living tissues which surround them. The articulations of this stem are usually very numerous, cylindrical, and present a series of rays striated upon their articulated faces. In _Pentacrinus_ they are prismatic and pentagonal; that is, they present five projecting angles, and on their articulated face a star with five branches, or, better still, a rose with five petals. At the base of the stem of this animal-plant, in many of the Crinoïdæ, we find a sort of spreading root, which is implanted in the rocks, and is capable of growing by itself, of nourishing the stem, and of producing new ones.