Mr. J. Ralfs on the Nostochinese. 341 



is the true Flos-aqua of almost every algologist prior to Lyngbye, 

 whose error has misled many succeeding writers and confounded 

 plants of widely different aspect. The descriptions of Linnaeus, 

 Roth and Agardh, although more or less deficient, agree far 

 better with this species than with any others which have been 

 confused with it. Lyngbye, indeed, suspected that his Nostoc 

 Flos-aqua was distinct from the plant of the two latter writers*, 

 an opinion confirmed by Agardh so far as regards himself. 

 Mr. Borrer has sent me a specimen of Byssus Flos-aqua distri- 

 buted by Mohr, who, there is every reason to suppose, was fully 

 acquainted with the plant then known by that name : the speci- 

 men, which is a very good one, scarcely differs even in colour 

 from those recently gathered by Professors Kutzing and Allman. 

 I cannot obtain the slightest clue to the Flos-aqua of our earlier 

 British writers. They give no habitats, and although the specific 

 definition of Hudson, Lightfoot and Withering agrees with this 

 species ("filamentis plumosis natantibus"), yet, as it is a mere copy 

 from Linnaeus, no dependence can be placed upon it. The two 

 former authors give no original remarks, and Withering' s own 

 observations agree but indifferently with his specific quotation ; for 

 his description, "jointed filaments straight or curled like a cork- 

 screw/' is more applicable to a Trichormus. 



Plate IX. fig. 6. a, portion of foreign specimen magnified ; b, Dub- 

 lin sp. ditto ; c, filaments highly magnified. 



2. A. cyaneum ( ). Filaments free, aggregated into a thin mucous 



stratum ; sporangia linear, eight to twelve times longer than broad, 

 furnished with a conspicuous hyaline covering. Limnochlide Flos- 

 aqua, $. hercynica, Kutzing, Species Algarum, p. 286 (1849) ; 

 Tabulae Phycologica?, t. 91. f. 11 ? 

 On aquatic plants in boggy pools at Llyn Gwernan and Dolmelynlyn 



near Dolgelley, J. R. 

 Germany, Kutzing. 



Stratum minute, thin, tender, of an opake light blue colour. 

 Filaments very slender, straight, nearly colourless, having a 

 slightly dotted appearance from the scattered granular endo- 

 chrome, not constricted at the dissepiments, which are very in- 

 distinct, and only to be detected by careful examination in a 

 favourable light ; ends obtuse, not attenuated. Joints or ordi- 

 nary cells nearly equal in length and breadth. Sporangia elon- 

 gated, cylindrical, generally solitary near the centre of each fila- 

 ment, but sometimes scattered, each inclosed in a broad, hyaline 

 covering. 



* " An sit Conferva Flos-aqua, Roth, Oscillatoria Flos-aqute, Ag., justo 

 ambigitur ; illae enim filis rectis et parallelis gaudere describuntur, haec vero 

 filis curvatis, implexis instructa est." — Lyngbye, Tentamen Hydrophyto- 

 logia? Danicaj. p. 202. 



