312 Marine Alga of Bemvick-on-Tweed. 



f. polystromatica, Batters, in Holmes's Alg. Brit. Exsicc. 



Thallus crustam formans multis stratis cellularum constructam. 

 Cetera ut in forma typica. Tab. Nost. xi., fig. 1a and b. 

 Exsicc. Rhododermis elegans, f. polystromatica, Holmes, Alg. Brit. Rar. 



Exsicc, no. 92. 

 Hab. On rocks near low-water mark. Rare. Fruit Jan. and Feb. 

 Berwick Bay. 



A rare species forming very thin crusts on rocks near low-water 

 mark. The fronds are roundish or indefinite in outline from half 

 an inch to a foot or more in diameter, composed of several layers 

 of cells, and not as in the typical form of two layers only ; the 

 cells of the thallus about -006 mm. long by -007 mm. broad ; the 

 sori usually very numerous, and produced on all parts of the 

 frond except the extreme margin ; the paraphyses short, stiff, 

 distinctly curved, about '064 mm. long by -005 or -006 mm. 

 broad ; the tetraspores large and cruciate about -026 mm. long 

 by -012 mm. broad. The thickness of the frond varies in 

 different individuals from -050 to -105 mm. 



I am indebted to Dr. Bornet for comparing specimens of my 

 Berwick plant with Orouan's original specimens of Rhododermis 

 elegans, and for pointing out that they belonged to the genus 

 Rhododermis, and not to Peyssonnelia as I had at first supposed. 

 I am also indebted to Mr. T. EL Buffham for taking measure- 

 ments of this and the next species. 



Rhododermis parasitica, Batters, in Holmes's Alg. Brit. Exsicc. 

 Thallus crustam parenchymaticam nigro-rubram formans 

 cellulis multis in seriebus verticalibus dispositis constructam ; 

 fills verticalibus '120 — 135 mm. longis, inferne "008 

 mm. crassis, superne -007 mm. crassis ; cellulis 

 cireiter -009 mm. longis. Tetrasporae circiter -028 mm. 

 longse, -012 mm. crassse, in soris superficialibus inter 

 paranemata -05 — -06 mm. longa, circiter -005 mm. crassa 

 simplicia, curvula, rigidiuscula evolutee. 

 Tab. Nost. xi., fig. 2a and b. 

 Exsicc. Rhododermis parasitica, Holmes, Alg. Brit. Rar. Exsicc, no. 93. 

 Hal). On the stems of Laminaria hyperborea. Fruit Jan. and Feb. 



Rare. Berwick Bay. 

 A thicker, darker coloured plant than Rhododermis elegans, and 

 so far as I have observed, always epiphytic on Laminaria hyper- 

 borea. The fronds form thin, dark-red, almost black crusts, 



