GG SYNOPSIS OF BRITISH SEAWEEDS. 



virgate, once or twice compounded ; pinnulse subulate or 



bifid, civet, closely sel ; the axils acute An. 8p. r. J., p. 54. 

 .Atlas, PL XXV. Pig. 108.) 

 Polyaiphonia criatata, Hart). Fucus cristatus, var. 7, Turn. Plo- 



eaniium cristatum, Lamour. 

 Hub. South of England and Ireland. On the rocky beds of 

 shallow tide-pools exposed at low-water to fidl sunshine, 

 among Coraltina officinalis, etc. Perennial? Summer. 

 A very rare plant on the British shores, though frequent 

 in the south of Europe. Our figure is made from a speci- 

 men gathered at Miltown Malbay, where, in one or two 

 stations, I was so fortunate as to meet with this beautiful 

 plant in considerable abundance. It completely clothed 

 the rocky bottom of a tide-pool four or five yards in dia- 

 meter and from three to six inches in depth. Where the 

 water became deeper the plant disappeared. The species 

 has a structure very similar to that of a Polysiphonia, in 

 which genus I formerly placed it. Indeed, except that we 

 have here an external coating of cells, there is nothing to 

 distinguish it from an ordinary Polysiphonia. 

 104. thuyoides (The cypress JRytiphlcea) ; stems erect, rising 

 from creeping fibres, terete ; below simple, and set with 

 short, spine-like ramuli ; above much branched ; branches 

 alternate, very erect, bi-pinnate ; pinnae multifid or pinnu- 

 late ; axils rounded ; ceramidia ovate, sessile, densely set, 

 Harv. in Mack. Fl. Hib. part 3. p. 205. (Atlas, PL XXIII. 

 Fig. 101.) 

 Grrammita rigidula, Bonnem. 



Hab. In pools left by the tide, growing either on the rocky bot- 

 tom or on Corallines and other small Algse. Perennial. 

 Summer. Abundant on the west coast of Ireland. 

 From Rytiphlcea complanata this species may always be 

 known by its darker colour, cylindrical stems, and gene- 

 rally by a narrower frond. In ramification and general 

 habit there is much similarity. The two may sometimes 

 be found growing in close proximity, and even mixed to- 

 gether, but I have generally observed that R. thuyoides, 

 which is the stiffest in substance, usually grows in the 

 shallow parts of the tide-pool, sometimes standing out of 

 the water, while R. complanata never dries during the 

 recess of the tide. Small specimens of Polysiphonia ni- 

 grescens much resemble the present species in habit, but 

 are at once known under the microscope by the very dif- 

 ferent structure of the frond. 



