Mr. II. J. Carter on the Antipatharia. 395 smooth surface and glassy lustre of fresh spicules ; the surface, indeed, differs very much as that of ground from polished glass. That they have exchanged the colloid for the crystal-line state is clearly shown by the elevation which has taken place in their refractive index and by the colours which they give with polarized light. The effects of solution are visible in little hemispherical pits which have been eaten in over the surface (fig. 46) , and by the irregular outline of some of the fusiform spicules, which appear in optical section as though irregularly scolloped. The canals of many are enlarged, but obliterated in the majority, probably as a result of secondary silicification. To secondary silicification we may also refer the tuberculation of some of the forms. Occasionally den-' drites of iron pyrites are seen shooting through the substance of the spicules, the first stage of a replacement which is found completed in spicules from other deposits. Probable depth of the Sea. — The sponges which furnished the spicules lived on a sea-floor probably somewhere between 100 and 400 fathoms deep. The Lithistida?, which have fur-nished so large a proportion of the spicules, have been dredged from depths varying between 75 and 374 fathoms. Lyidium torquilla, which so closely resembles the fossil Podapsis, was obtained from a depth of 270 fathoms. Of other sponges the recent Pachastrella geodoides, which our P. globiger resembles, was dredged from 292 fathoms, and Geodia Macandrewi, which is represented by the fossil Q, cretaceus, from 100 to 270 fathoms. [To be continued.] XL VIII. — Additional Observations on the Antipatharia. By H. J. Caeter, F.R.S. &c. By reference to the footnote at page 304 of the last number of the ' Annals,' it will be seen that I had not then read Lacaze-Duthiers's memoirs " Sur les Antipathaires " (in the ' Annales des Sciences Naturelles, Zoologie,' tomes ii. and iv. pp. 169 and 1 of 1864 and 1865 respectively) at the time that I finished my short article on the Antipatharia, chiefly questioning the nature of the polyp (viz. whether Hydroid or Actinoid?), and stating, at page 302, that MM. Milne-Edwards and Jules Haime, in 1857, had summed up our knowledge on this point in the following way, viz. : — â– " Jusqu'ici on n'a pas etudie l'anatomie de ces animaux, et on 28*
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