NEW OR CRITICAL BRITISH MARINE ALGJE. 389 Cm. These differences, however, seem to me to hardly do more than mark stages in the development of a single species. 14. Ehododermis elegans Crn. F'lor. Finist. 148, t. 19, fig. 130. On old shells dredged from the " Queen's Ground," Plymouth, G. Brehner S E. A. B. Plymouth specimens of this species agree in every respect with the French specimens gathered by the Crouans. The vegetative portions of the frond are monostromatic, and it is only beneath the tetrasporic sori or where one frond overlaps another that the thallus is composed of more than one layer. On the other hand, the frond of the plant formerly described by me as a variety, polystromatica, of this species is always composed of several layers of cells, and the whole plant is so unlike typical R. elegans that, following the advice given me by the late Prof. Schmitz, I propose to raise it to specific rank as R. poly sir omalica. At one time Prof. Schmitz thought my R. parasitica and R. polystromatica sujQficiently different from 7^. elegans, the only species of the genus previously known, to justify the formation of a new genus for their reception. Shortly before his death, however, he wrote to inform me that on again looking into the question he had come to the conclusion that I was right in placing them in the genus Rhododermis, as the differences were hardly generic. 15. Rhodochorton parasiticum, sp. n. {R. sparswn Batt. List of Mar. Alg. Berw., non Call, sparsum Carm.). Fronds forming small, scattered, frequently confluent, velvety, carmine patches on the stems of Laminaria hyperborea {Cloustoni), composed of erect, free filaments from 1 to 5 mm. in height, which arise from endo- phytic filaments penetrating the tissues of the host-plant to a depth of from 200 to 500 /x and more. Endophytic filaments simple or branched, irregularly swollen here and there, either singly breaking through the cortical layer of the host-plant and then at once sending out compact tufts of free filaments, or first uniting laterally so as to form solid, roundish, oblong or irregularly-shaped masses from 100 to 150 /x in diameter, from which the erect free filaments arise ; in both cases the endophytic filaments or cell-masses near the surface of the host-plant ultimately become confluent, and form a sort of pseudo-parenchymatous layer of considerable extent, which unites the several tufts of erect filaments. Cells of the endophytic filaments very irregular in shape and size, usually more or less angular, 3-30 fx long, and from 4 to 18 /x in diameter, the cells terminating the endophytic filaments downwards often sharply pointed. Erect filaments about 15 /x in diameter, simple or sparingly branched, branches long, erect, usually simple ; cells in the centre of the filament from 1^ to 4 times longer than broad, those towards the apices of the filaments much shorter. Tetraspores about 24 fx long by 15 or 18 /x wide, borne on tufts of short, simple, forked or corymbose, opposite or alternate, few-celled special branches produced near the apices of the erect filaments. Berwick, Dunbar, &c., E.A.B. I am indebted to the courtesy of the Director of Kew Gardens for permission to examine the type-specimens of Carmichael's
