The genera Millepora and Cellepora have not been found in a fossil state sufficiently distinct to satisfy mi neralogists respecting these. But a species of Isis has been found fossil in Sicily. It is equally doubted, whe ther any of the genera Antipathes and Gorgonia have been discovered as fossils.
A fossil occurs not very unfrequently in flints, the living nature of which is unknown, as none such has been found in the natural state. It consists of numerous small oblate spheroids connected together by filaments, and generally distributed in layers in the flints; and we need not repeat the conjectures that have been offered respecting them, such as, that they were ova, or that they are not animals. A very admirable figure of this fossil will be found in the Transactions of the Geological Society.
The genus Alcyonium, often found in the fossil state, comprises those fossils which have so often been mistaken for fruits, such as, figs, pears, &c. With respect to the true genera of these, as thus found, there has often been much doubt, as sponges and other marine productions seem to have been sometimes confounded with them; while, with respect to many others, it is scarcely possible to refer them to any living genus. In the natural state, the alcyonium is a spongy or gelatinous body, having a cellular integument which contains polypi, and it occurs under various shapes, so as to form a great number of species. Sponges are, on the contrary, fibrous ; yet it is sometimes difficult to distinguish some of the species from some in the former genus, even in the recent state, and hence the great difficulty of doing it when petrified. For the present, therefore, all the fossils of this general cha racter are unavoidably united. Among the species, the ramified are most rarely fossil. One resembling the Alcyonium digitatum occurs in some limestones, and the simple elongated ones are not uncommon. Another occurs which has been compared to a quince, and another, again, resembles a fig ; these being among the pedicellated kind. But it is useless for us to proceed with any farther account of this almost endless genus ; as the variety is such as to defy all description, and as scarcely even figures could convey an adequate conception of them. We shall only remark, that this is one of the fossils which is peculiarly subject to be imbedded in flint, a circumstance which has been a source of much difficulty to mineralogists, and that many flints have their shapes determined precisely by the extent of the animal.
Near Maest•icht are found numerous fossils, the genera of which have been a source of much doubt and disputa tion among mineralogists. They have been found to resemble flustra and various other living genera, while some again appear as yet to have no living analogies. For the same reasons, we need not attempt descriptions of these.
The encrinites and pentacrinites, also called trochites, &c. form one of the most numerous of all the tribes which are found in the the fossil state ; and the enormous quan tities in which they are found must excite surprise.
These animals are of a very singular construction, being formed of innumerable joints, following each other like the vertebra of fishes, and all of them perforated by some starry form. In the encrinites, the joints are round, in the pentacrinites they have five angles, and the separate parts are sometimes called trochites, entrochi, and asteria. These animals are simple, or ramified, and sometimes they have heads, or bodies, distinct from what may be called the trunk and limbs. In the living state, some species are known in the West Indies. As thirty or forty kinds, or more, have been found in the fossil state, we can only name one or two of the most remarkable in this place.
The lily encrinite, or stone lily, as it has been called, is one of the most remarkable of these, and it occurs in Eng land. The remarkable circumstance in this is, that its arms are furnished with a sort of hand, formed of joints that close up like the calyx of some flowers. The cap encrinite of Derbyshire is another remarkable species, the hand part being folded up in a more globular or compact form. Others, differing in this part, are known by the naine of the turban and the pear encrinites. But these are endless. The plumose is one of the most remarkable, on account of the beauty and delicacy of its ramifications, and that which is called the Briarean is also amongst the most conspicuous species ; but as we have no room to prolong this enumeration further, we will only remark, that these animals, or their detached vertebra, are the frequent sources of ornamental marbles. In Northumberland, they are known by the name of St. Cuthbert's beads ; and it is supposed by the common people that they have certain living powers, as when placed on a plate or smooth surface, with some vinegar, they move ; in consequence, it is plain, of the disengagement of bubbles of carbonic acid at their inferior surfaces.