_Lign. 75, fig. 4_, represents the usual appearance of a flint deriving its form from a Choanite; _fig. 2_, is the upper part of a Choanite preserved in chalk, and richly coloured by iron; the opening at the summit, _a_, is the orifice of the central cylindrical cavity, which is in this instance filled up by chalk, but in flint specimens, with silex of a different colour to that of the surrounding mass. If _fig. 2_, were placed on the top of _fig. 4_, the general shape of the original zoophyte would be represented. The opening at the base of _fig. 4_, marks the spot whence the processes of attachment proceeded. The vertical section of a flint, similar to _fig. 4_, is shown at _fig. 3_; and in this example are seen the central cavity, and a section of the substance of the zoophyte, which is traversed by numerous tubes, that ramify through the mass of which the body was composed, and terminate in openings on the inner wall of the central cavity, or sac. A transverse section of a similar flint is delineated in _fig. 1_; the central white spot indicates the sac filled with flint, and the tubes are seen radiating from it through the mass; under a powerful lens the interstitial structure appears to be granular rather than porous. The perfect transparency of the body when silicified, and the rich tints it has acquired from metallic solutions, and the compressed state in which it is often found, seem to indicate that the original mass was a soft gelatinous substance, like that of the _Actinia_, strengthened by spicula; for numerous tri-radiate spines, like those on the left-hand of _fig. 5, Lign. 75_, occur occasionally in chalk specimens. In many Choanites, which differ in no other respect from the present species, vertical sections show on each side the central cavity, large oval spots, that are sections of a canal which traverses the entire mass, proceeding from the base to the summit, in a spiral coil around the central cavity. This structure was first detected by Mr. Cunnington. Mr. Woodward thinks this spiral tube is common to all the Choanites, and constitutes a generic character; but so many examples have passed under my examination in which no traces of such a canal are perceptible, that it may be a specific difference. Among the chalk amorphozoa whose true affinities are doubtful, is a small turbinated zoophyte, which I would place provisionally under this genus; it has a shallow central cavity, with a broad smooth margin, a reticulated external surface, and radicle processes proceeding from the base; see _Lign. 80, fig. 1_. [Sidenote: PARAMOUDRA.]