HEW OR CRITICAL BRITISH MARINE ALG£. 387 more or less swollen here and there, much and irregularly branched, interwoven, forming a network from which very short, few-celled, erect filaments arise, and breaking through the cortical layer of the host-plant terminate in a sporangium ; cells of the decumbent filaments 6-18 /i long by 3 /x in diameter, those of the erect fila- ments about as long as or a little longer than broad, and of about the same diameter as the decumbent filaments ; monospores nearly globular, about 6 /x in diameter, terminating the erect filaments, which are composed of from one to three or four cells. In the cortical layer of Dasya coccinea. Plymouth, (r. Brebner. This minute species bears the same relationship to the other species of Acrochcetium that Rhodoclwrton mcmhranaceiim Mag. does to the other Rhodochortones. 10. Peyssonnelia rupestris Crn. Flor, Finist. 148, tab. 19, gen. 129. On old shells dredged from the ** Queen's Ground," Plymouth. I detected this pretty little species on some old shells sent to me from Plymouth by Mr. Brebner. The species is dis- tinguished from the other Peyssonnelia! by the very thin frond firmly adherent to the substratum, and entirely destitute of rhizoids ; by the almost square cells of the thallus, the comparatively very large tetraspores, and the short paraphyses, which are about as long as the tetraspores, and, except in their greater slenderness, but slightly differentiated from the thallus-filaments. 11. Cruoriopsis Hauckii, nov. nom. = Ct-itoneUa artnorica Hauck, Meeresalg. 81, non Crouan, Ann. Sc. Nat. 4th ser. xii. t. 22, fig. G. 84-37, nee Crn. Fl. Finist. 148, t. 19, gen. 128. Fronds forming thin, crust-like, purple-red expansions, closely adherent to the substratum, roundish or irregular in outline, from 1 to 8 mm. in diameter, and from 50 to 100 ft thick ; the younger fronds fre- quently overlapping the older ones ; cells at the base of the erect filaments 10-15 fj. in diameter, and about as loug as or a little longer than broad, those towards the apices three or four times longer than broad, and only 4 or 6 /* in diameter ; tetraspores immersed in the substance of the frond, 24-80 /i long by 15-20 /x in diameter, irregularly divided, terminal on shortened thiUlus- filaments. On stones dredged off the west end of the breakwater, Plymouth, G. Brebner. As originally described by the brothers Crouan, the genus CruoneUa appears to be very closely related to reyssonneli<i, and to differ from it only in the slightly different form of the paraphyses and the fan-shaped disposition of the cell-rows of the basal layer, characters which induced the late Prof. Schmitz to refer the well- known Peyssoniu'lia Dubyi Crn. to this genus. On the other hand, the plant described by Hauck as Cnionella annorica is evidently not the same as that described by the Crouans under the same name, but is much more nearly related to Cruonopsis cruciata Duf., as the tetraspores are immersed in the substance of the frond, not produced in superficial nemathecia as in Cruoriella, and the thallus- filaments are only loosely united to one another, while in Cruoriella they are firmly united into a more or less parenchymatous layer. From Cruonopsis cruciata it is distinguished by the much larger
