The ground-mass or matrix of the Boghead is referred to a brown ulmic precipitate thrown down on the floor of a Permian or Carboniferous lake, probably under the action of calcareous water. In this material there accumulated countless thalli of minute gelatinous algae, which probably at certain seasons completely covered the surface of the waters, as the _fleurs d’eau_ in many of our fresh-water lakes. In addition to the thalli of _Reinschia_ and _Pila_ the Bogheads contain a few remains of various plant fragments, pollen-grains, and pieces of wood. Fish-scales and the coprolites of reptiles and fishes occur in some of the beds. On a piece of Kerosene shale in the Woodwardian Museum, Cambridge, there are two well-preserved graphitic impressions of the tongue-shaped fronds of _Glossopteris Browniana_, Brongn. There can be little doubt that the beds of Boghead were deposited under water as members of a regular sequence of sedimentary strata. The yellow bodies which form so great a part of the beds are practically all of the same type. _Reinschia_ and _Pila_ cannot always be distinguished, and it would seem that there are no adequate grounds for instituting two distinct genera and referring them to different families of recent algae. Stated briefly, my conclusion is that the algae of the French authors may be definite organic bodies, but it is unwise to attempt to determine their affinities within such narrow limits as have been referred to in the above _résumé_. The structure of the bituminous deposits is worthy of careful study, and it is by no means impossible that further research might lead us to accept the view of the earlier investigators, that the brightly coloured organic-like bodies may be inorganic in origin. D. RHODOPHYCEAE. (FLORIDEAE. RED ALGAE.) The thallus of the members of this group assumes various forms, and consists of branched cell-filaments of a more or less complex structure. Cells of the thallus contain a red colouring matter in addition to the green chlorophyll. The reproduction is asexual and sexual; the formation of asexual reproductive cells (_tetraspores_) in groups of four in sporangia is a characteristic method of reproduction. Sexual reproduction is effected by means of distinct male and female cells. With the exception of a few fresh-water genera all the red algae are marine. The Rhodophyceae, like the Cyanophyceae and Chlorophyceae, include a shell-boring form which has been found in the common razor-shell[343]. Several genera live as endophytes in the tissues of other algae. The recent species of this section of algae are characteristic of temperate and tropical seas. One subdivision of the red algae, the Corallinaceae, is extremely important from a geological point of view and must be dealt with in some detail. CORALLINACEAE.