We miss here the two great Molluscan groups of the creeping Sea-snails like the limpet and whelk, and of the ordinary bivalves like the oyster and cockle. Both are present in the lowest Cambrian, though in small numbers compared with their present abundance. Possibly they had not yet appeared in the Etcheminian Sea, though the muddy and sandy bottoms, evidenced by its slates and sandstones, would seem to have afforded favourable habitats, and warrant the expectation that species may yet be found. The case was different with the little group of the Lamp-shells, or Brachiopods. These creatures, somewhat resembling the ordinary bivalves in their shelly coverings, were very dissimilar in their internal structure, and once settled on the bottom they were attached for life, not having even the limited means of locomotion possessed by the Sea-snails and common bivalves. They collected their food wholly by means of currents of water produced by cilia, or movable threads, on arms or processes within their shells. In this they resembled the young or embryo stages of some of the more ordinary Mollusks, though they are so remote from these in their adult condition that they have usually been placed in a distinct class, and some naturalists have thought it best to separate them from the Mollusks altogether. Their history is peculiar. Coming into existence at a very early date, they became very abundant in early Palæozoic times, then gradually gave place to the ordinary bivalves, and in the modern seas are represented by very few species. Yet while in the middle period of their history they are represented by very many peculiar specific and generic forms. Some of the earliest types, like Obolus and Lingula, persist very long, and the latter has continued without change from the Early Cambrian to the Modern period. The great group of the Sea-stars and Sea-urchins appears only in a few of its lower forms, and seems to be the only class represented by embryonic types. The coral animals are absent, so far as known. The Jelly-fishes and their allies cannot be preserved as fossils, but some peculiar markings, at one time regarded as plants, are now supposed to be trails made by the tentacles of creatures of this kind moving over muddy bottoms. A few spicules indicate Sponges, and the ubiquitous groups of the marine Protozoa, the Foraminifera and the Radiolaunus, are represented by shells scarcely distinguishable from those of modern species. The great and peculiar forms represented at this early time by Cryptozoon and its allies seem long ago to have perished, and we shall have to return to them in a later stage of our inquiry.