The Globigerinoe, Cyatholiths, Coccospheres, Discoliths in the one are absolutely identical with those in the other; there are identical, or closely analogous, species of Sponges, Echinoderms, and Brachiopods.

It is a Brachiopod; a family with which the ancient seas once swarmed, but which is rare now, all over the world, having been supplanted and driven out of the seas by newer and stronger forms of shelled animals.

The nearest spot at which you are likely to dredge a live Brachiopod will be in the deep water of Loch Fyne, in Argyleshire, where two species still linger, fastened, strangely enough, to the smooth pebbles of a submerged glacier, formed in the open air during the age of ice, but sunk now to a depth of eighty fathoms.

When named with reference to their double shells, they are called Bivalves; and with them are associated a host of less conspicuous animals, known as Ascidians, Brachiopods, and Bryozoa.

Brachiopods formed another of his classes; but these differ from the other Bivalves only in having a net-work of blood-vessels in the place of the free gills, and this is merely a complication of structure, not a difference in the general mode of execution, for their position and relation to the rest of the organization are exactly the same in both.

Pteropods constituted another class in his division of the type of Mollusks; but these animals, again, form only an order in the class of Gasteropoda, as Brachiopods form an order in the class of Acephala.