NEW OR CEITICAL BRITISH MARINE ALGiE. 389 



Crn. These differences, however, seem to me to hardly do more 

 than mark stages in the development of a single species. 



14. Rhododermis elegans Crn. Flor. Finist. 148, t. 19, fig. 130. 

 On old shells dredged from the " Queen's Ground," Plymouth, 

 G. Brehier d E. A. B. 



Plymouth specimens of this species agree in every respect with 

 the French specimens gathered hy 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, pobjstromatica, 

 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 li. polystromatica. At one time Prof. Schmitz thought my 

 It. parasitica and R. polystrumatica suflficiently different from R. 

 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 Rliododermis, as the differences were 

 hardly generic. 



15. Rhodochorton parasiticum, sp. n. {R. sparsrmi Batt. List 

 of Mar. Ahj. Jlerw., non Call, sparsum Carm.). Fronds forming 

 small, scattered, frequently confluent, velvety, carmine patches on 

 the stems of Laminaria hyperborea [Gloustoni), 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 /z 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 jj. 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 jjl long, and from 4 to 18 /^ in diameter, the 

 cells terminating the endophytic filaments downwards often sharply 

 pointed. Erect filaments about 15 /a in diameter, simple or 

 sparingly branched, branches long, erect, usually simple ; cells in 

 the centre of the filament from li to 4 times longer than broad, 

 those towards the apices of the filaments much shorter. Tetraspores 

 about 24 p. 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., Fj. A. B. 



I am indebted to the courtesy of the Director of Kew Gardens 

 for permission to examine the type-specimens of Carmichael's 



