^{page 310 note 1} “There is no class of animals in which the form varies to so great an extent (as the Irving sponges) according to difference of locality or other circumstances; and even where there is a striking normal form, it is rarely thoroughly developed until the animal has reached its full maturity,” Spongiadæ (Ray Soc.) vol. i. p. 3. “As a generic character, form is inadmissible, inasmuch as each variety of it is found to prevail indiscriminately in genera differing structurally to the greatest possible extent.” Ibid. p. 156.

^{page 311 note 1} Paléont., iv. 2nd ed.

^{page 311 note 2} E'ponges Fossiles, 1859.

^{page 311 note 3} Classification des Spongiaires du Haut Jura, and E'tudes Paleont. sur le Haut Jura, p. 139.

^{page 311 note 4} Mikroskopische Untersuchungen ueber den innern Bau einiger fossilen Schwamme Z. W. Z., etc.

^{page 311 note 5} “Qu'ils n'ont jamais éte conées, mais que leur tissu à toujours átá calcaire et pierreuse.” Cours Elementaire de Paléontologie, torn. ii. p. 208.

^{page 311 note 6} l. c., p. 5.

^{page 312 note 1} The compression often observed in fossils, especially those of the older rocks, is probably due to the squeezing to which they hare been subjected in the change of position and contortion of the beds in which they occur, rather than to the dead weight of the superimposed sediment. It is now well known that Starfish and other soft animals, even at the great depths of mid-ocean, are not compressed, owing to the pressure being applied equally on all parts. Prof. Sars dredged sponges, actinozoa, true molluscs and worms at a depth of 300 fathoms; and the Swedish deep-sea dredgings, in the expedition to Spitzbergen, brought up Crustacea, mollusca, and annelids, at depths of from 6000 to 8400 feet. Quoted in Intellectual Observer for December, 1866, p. 400, from Annals of Nat. History.

^{page 313 note 1} l. c. p. 154.

^{page 313 note 2} Both Ischadites and Ptylospongia occurred ta Eichwald sometimes calcified, and sometimes converted into bisulphnret of iron, mote or less peroxidized. His Manon deforme, from Gherikoff, was silicified, while the examples of the same species from the environs of Poulkowa were all calcified. Lethæa Rossica, p. 339. Ischadites Kænigii occurs in our British Upper Silurian rocks, both as a calcareous and as a pyritized fossil.

^{page 313 note 3} De la Beche, Mem. Geol. Surv., vol. i., p. 273.

^{page 314 note 1} “Lectures on Chemistry,” p. 491.