THE ANNALS 



AND 



MAGAZINE OF NATURAL HISTORY, 



No. 69. MARCH 1843. 



XXV. — On a new Genus of Algae belonging to the family of 

 the Nostochinae. By Geo. J. Allman, A.B., L.R.C.S.I., 

 Secretary to the Dublin Microscopical Society*. 



[With a Plate.] 



In the early part of October 1842, I observed a substance of 

 a pea-green colour abundant in the water of the Grand Canal 

 Docks near Dublin. This substance was unequally distri- 

 buted, being in some places collected in large quantity, while 

 in others the water was quite free from it. It consisted of 

 flocculent unattached masses varying much in size and occu- 

 pying very different depths, some floating upon the surface, 

 while others were observed suspended in the water, and might 

 be traced downwards till the depth alone concealed them from 

 the sight. 



The general appearance of these masses, so far as their me- 

 chanical arrangement was concerned, might remind one of 

 certain substances in the act of precipitation from their solu- 

 tions, as camphor when undergoing precipitation from alcohol 

 by the addition of water, or soap when separated by an acid 

 from an aqueous or alcoholic solution, or perhaps still more 

 of the curd of milk when diffused through the uncoagulable 

 part of the fluid. In some places the green matter had been 

 left by the retiring water upon the stones of the margin, and, 

 here drying, had assumed a beautiful bluish green or verdigris 

 colour without lustre. 



On subsequently visiting the Canal Docks at several differ- 

 ent periods, I observed that the substance under consideration 

 appeared sometimes in but very small quantity, while on other 

 occasions it was to be seen much more abundantly. This ap- 

 pearance and disappearance of the green matter would seem 

 to be independent of the direct rays of the sun, and is pro- 

 bably the result of barometrical and other meteorological in- 

 fluences. 



* Read before the Society on the 1st of December 1842. 



Ann. fy Mag. N. Hist. Vol. xi. M 



