NEW OR CRITICAL BRITISH MARINE ALG^. 439 



subgenus — Erythwclathrus — is said to be distinguished by the 

 presence of paraphyses, but probably empty sporangia have been 

 mistaken for these organs. The present species belongs to the 

 second subgenus, and is distinguished by its thin, brownish fronds 

 and slender, spindle-shaped, regularly zonate tetraspores. Under 

 the name H. rubra, the brothers Crouan sent specimens belonging 

 to more than one undescribed species to Prof. J. Agardh, who 

 named and described them. The Crouans, however, seem to have 

 failed to recognize the plants from Agardh's descriptions, and much 

 confusion has arisen owing to their having applied the Agardhian 

 names to species which Agardh did not intend to indicate by them. 

 That I might not add to the confusion, I sent specimens and micro- 

 scopic preparations to Prof. Agardh, and requested him to compare 

 them with his type specimens ; this he has most kindly done. Dr. 

 Bornet has also been good enough to compare British specimens of 

 HcBinatophlcea Crouani Crn. (non J. Ag.) with authentic specimens. 

 I am therefore in a position to clear away some of the doubts sur- 

 rounding this species. Hildenhrandtia (HcematoplUcea) Crouani J. Ag. 

 is identical with //. rosea Crn. Fl. Finist. p. 148, tab. 19, gen. 126, 

 while llcematophlcea Crouani Crn. Ann. Sc. Nat. 4 ser. Bot. vol. ix. pi. 3, 

 fig. Q, a b c, is Hcematocelis rubens J. Ag. Spec. Alg. vol. ii. p. 497, 

 which is thus recorded under two different names in the Fiorule du 

 Finistere. It may be useful to point out that Hauck's description 

 {Meeresalg. p. 38) of the tetraspores of H. j)rototypus Nardo was 

 most probably drawn up from a specimen of H. Crouani, Hauck 

 having mistaken the true (irregularly divided) tetraspores of H. 

 prototypus for carpospores. The late Dr. F. Schmitz informed me, 

 in conversation, that Dr. Hauck had no authority for saying that 

 he (Dr. S.) had seen the cystocarps of any species of Hildenbrandtia, 

 which so far as he knew were quite unknown. 



Porphyrodiscus, nov. gen. Fronds crustaceous, forming 

 smooth, firm, cartilaginous, roundish expansions, closely adhering 

 to the substratum by the entire under surface. Cells small, of 

 nearly the same size in all parts of the frond, firmly united into a 

 pseudo-parenchymatous layer. Tetraspores regularly zonate, formed 

 in external, hemispherical or flat wart-like protuberances (nema- 

 thecia). Paraphyses wanting or not observed. Cystocarps unknown. 



19. P. simulans, nov. spec. Fronds dark shining purplish- 

 red, roundish, about 1 inch in diameter, and from 150-300 p. thick. 

 Cells small, about as long as broad, 4-6 p wide. Nemathecia 

 hemispherical or flat, from 150-300 p. in breadth. Tetraspores 

 slender, spindle-shaped, regularly zonate, 20-25 p, long by 5-8 p. 

 wide. Hab. : On rocks near low-water mark, Berwick, February, 

 1889, E. A. B. 



To the naked eye this species resembles dark-coloured specimens 

 of HUdenbraiidtia prototypus ; but the tetraspores, instead of being 

 contained in cavities sunk beneath the surface of the frond and 

 entirely enclosed, with the exception of a minute pore communi- 

 cating with the surface, as in the genus Hildenhrandtia, are formed 

 in external hemispherical or flat nemathecia, surrounded by a more 



