The Squamariæ resemble lichens in spreading themselves in a red crust over stones and rocks. They have roots below, and warts, on their upper surface, in which there are tufts of moniliform spore-bearing threads. The tetraspores of Cruoria pellita are shown in fig. 26 D; its repeatedly forked filaments taper upwards, and the tetraspores are formed in the swollen centre cell of the filaments. The Peyssonnelia grows on shells and other marine objects, and extends from the Mediterranean to Ireland, and the east coast of North America. The Polyides rotundus (fig. 23 A), representing the only genus of the Spongiocarpeæ, has a dark purple solid gristly cylindrical stem, repeatedly and regularly forked, all being of the same thickness. The tips of the last forkings, which are small and equal, give the top of the plant a rounded form. The microscope shows that the stem and branches are composed of a central column of interlaced threads and radiating cells; it shows, moreover, that hyaline nuclei containing a cluster of conical spores whose broad bases radiate in all directions from a centre, as in fig. 23 _a_, are scattered among the articulated threads of oblong irregular spongy warts which clasp or embrace the stem and branches. The tetraspores are buried in the ends of the last forks. This plant is so like the Furcellaria fastigiata (fig. 23 B), that it affords a remarkable instance of similarity of form and total diversity of fructification, not only in the spores and their arrangements, but in the form of the tetraspores; for in the Polyides they are formed by two sections, one vertical and the other horizontal, while in the Furcellaria the endochrome is divided by three annular sections, as in fig. 23 E. The Gelidium corneum, common in Britain and almost everywhere, representing the group Gelidiaceæ, is opaque, firm, and of a dark purple. The axis with its alternate and repeated branches lying all in one plane, is composed of confervoid threads. This plant is distinguished by having its spore-cases or nuclei divided into two chambers by a fibro-cellular substance; the spores are either attached to this or to a network of threads; these bodies and the tetraspores are lodged in the tips of the branchlets. It is one of the most variable of all Algæ.