^{page 343 note 1} l. c., p. 17.

^{page 344 note 1} l. c., p. 146.

^{page 345 note 1} The Jerea pyriformis (Lamouroux) is perhaps a distinct species.

^{page 346 note 1} It is to this closer superficial portion of the tissue that M. Etallon has applied the name of périenchyma. “Dans certains cas,” he observes, “lorsque le spongiaire parait avoir acquis tout son développement, le tissue devient plus fin, plus serré, recouvre toute la surface d'one couche plus ou moins épaisse et adhérente et donne au squelette un aspect différent de celui qu’il avait a l'époque de la croissance et qu'on peut toujours retrouver par des coupes ou par l'usure.”—Rayonne's du Corallien (Haut Jura), p. 139; also Sur la Classification des Spongiaires du Haut Jura, p. 137.

^{page 347 note 1} Quart Journ. Geol. Soc., vol. x., p. 196.

^{page 347 note 2} It is not here necessary to discuss the question of a “dermal membrane,”as this would of course perish with the sarcode, and about which, moreover, some difference of opinion appears to exist, the facility with which the pores open and close to admit or check the incurrent streams of water, and the readiness with which the sarcodal mass is repaired after injury, and unites on contact with that of another individual of the same species, are facts which have been held to militate against the possession of such a structure. That the supporting tissue, in certain recent species, becomes closer and is otherwise modified at the surface, is clearly ascertained (see Bowerbank. Ecronemia acervous, Bowerb., MSS., l.c., p. 173, pl. 28, f. 355; also pp. 107, 108, pl. 20, f. 309 and 310; Halichondria panicea, Johnston, pl. 19, f. 303), and in some species there is a crusticular layer of embedded ovaries abounding in minute spieula (Bowerbank, l.c., Pachymatisma Johnstonia, Bowerb., p. 172, pl. 27, f. 353; Geodia. Barretti, Bowerb:, MS., p. 169, pl. 28, f. 354) beneath the surface of the sarcode. There is likewise a sponge common on the coast at Tenby, in which, in some individuals, the base and for a little distance above it does appear, in the dried condition, to be invested by something like a membrane, which terminates upwards in a welldefined and thickened or slightly wrinkled margin; the kerato-spicular tissue of the sponge immediately beneath it is more densely reticulated than in other parts of the animal; but I was unable to satisfy myself that it constituted a true membrane as distinct from the sarcode. That this soft structure may, under favourable circumstances, so impress the mould of the fossil as to produce the appearance described as an epitheca, may be possible; but this is altogether different from the sclerotic sheath which invests the exterior in the Zoantharia.

^{page 348 note 1} l. c., p. 113. Here we have an example of an oscule passing into a cloaca as age advanced, and an amorphous sponge becoming a fistulous one.

^{page 349 note 1} The Clionidœ are, however, only the accidental occupants of the cavities in which they are found, having located themselves in the excavations formed by Annelida and the terebrating mollusks. For the most part they are spicular sponges.

^{page 349 note 2} In some stellate spicula, probably in all, at the point where the central canals of the rays unite in the nœud, there is an hexagonal space, as noticed by this author, but the appearance of vertical and horizontal laminæ are referable to an optical effect of light.

^{page 349 note 3} l. c., p. 5.

^{page 350 note 1} These “Notes” were written in the year 1866.

^{page 350 note 2} Two undescribed species of this genus occur in the Lower Ludlow rocks of Leintwardine, for one of which I propose the name of P. Ludense, and for the other P. maculœformis. In P. Ludense the sponge has the figure of a horn slightly curved, and attains a height of 10 or 12 inches, and a transverse diameter (in its compressed state) of 4 or 5 inches. It consists of vertical and transverse fibres, which intersect each other obliquely at the base, but become more or less horizontal as the sponge enlarges; it is not evident, however, whether these fibres were united at the points of intersection, or simply apposed. The fibres which emanate from the base ascend to the summit, but as the sponge enlarged other fibres became intercalated, and scattered stellate (four-rayed ?) spicula occur in the interspaces. In all the specimens hitherto met with the sponge is completely flattened, but its original cup-shaped figure is shown in a specimen in the Ludlow Museum, in which a thin plate of compressed sediment which filled the cavity exhibits the fibres on either side; and in the P. fenestralis of the Lingula Flags, the same can be ascertained by making transverse sections, when the cut ends of the rods are shown ranged in parallel rows on either side of a lamina of the matrix which occupied the cavity, reduced to a mere plate by compression. The other species, P. maculœformis, occurs as semi-circular or semi-oval stains on the surface of the Lower Ludlow shales, about 1½ inches in height and an inch in transverse diameter. As in the former species, it consists of extremely delicate vertical and transverse fibres, with a few stellate spicula in the interspaces. So thin is the fossil that it might readily be mistaken for mere vegetable stains, unless the fibres are especially sought for with a magnifying glass, and its cup-shaped form is inferred only from the type to which the sponge evidently belongs.

^{page 351 note 1} Placed doubtfully among the Zoantharia, by M. Edwards and Haime, but specimens of this fossil from the Great Orme's Head, better preserved than De Koninck's types, now in the British Museum, enable the author to assign them a place among the sponges.