Gorgonia.--Of the flexible anthozoan coral, which from the flabellated form of the polyparium is generally called "Venus's fan," and by naturalists _Gorgonia_, a few fossil species have been discovered and determined. From the friable arenaceous limestone beds of Maestricht, which abound in corals, fine specimens of a delicate species are occasionally procured. _Wond._ p. 320, _fig._ 5, shows the character of this fossil zoophyte. Fossil Bryozoa. [Sidenote: FOSSIL BRYOZOA.] The second class of Polypifera, the Bryozoa or _Polyzoa_, are of a much higher order of organization than those which have engaged our attention. The body is not symmetrical, nor capable of contraction and expansion, as in the Anthozoa: it consists of a digestive cavity or sac, which is bent on itself and open at both extremities. The outer integument is either membranaceous or horny; sometimes calcareous. The oral aperture or mouth is surrounded by a circle of tentacula, from eight to twelve or more in number, and these tentacles are clothed with vibratile cilia. (_Wond._ p. 606, the polype of _Flustra pilosa_.) The polypes in this order never occur singly; they are always united by a common integument, but each enjoys an individual existence. The animal can extend its tentacula and protrude the mouth from the cell, but the rest of the body is incapable of extension or contraction. These polypifera increase by germination. In their organization, they so closely approach the mollusca, that in recent zoological systems they are placed in that class. The ciliated character of their tentacula has also led to their being named _Cilio-branchiata_. But as it is desirable in a work of this elementary nature to avoid conflicting opinions as much as possible, the fossil Bryozoa will be considered as corals, in the general sense of that term. [Sidenote: FLUSTRA. ESCHARA.] Flustra (_Sea-mat_). _Lign. 89, fig. 4, 5._--The polyparium is either membranaceous and flexible, calcareous and encrusting, or foliaceous, composed of cells, arranged in juxtaposition, more or less quadrangular, flat, with a distinct border, disposed on a flat surface, or on opposite surfaces, as in the _F. foliacea_. This is one of the most common genera of the encrusting and frondescent zoophytes. The _Flustra_ consists of a cluster, or aggregation of polypes, invisible to the naked eye; under the microscope, the polype is found to be a transparent gelatinous body bent on itself, with a sac or digestive cavity, having two apertures, the external margin of which terminates in eight or ten tentacula, clothed with cilia; the whole is surrounded by a firm wall, constituting a cell, from which the animal can protrude its tentacula and upper part. (Figures of the living polypes of Flustræ, _Wond._ p. 605, _pl._ vi. _fig._ 6, 7.)