20 Dr. Dickie 07i the Colour of a Freshwater Loch. 



Hon, radiating lamellae forty-eiglit, thin, twenty-four of which 

 reach the centre, while the intervening ones are nearly mar- 

 ginal, not reaching half-way to the inner zone ; interlamellar 

 vesicular plates very numerous and delicate in the outer zone, 

 apparently absent in the inner zone. 



This species has some affinity with the N. minus (M^Coy), but 

 is constantly distinguished by the open, simple, subseptate cha- 

 racter of the inner zone in the vertical section, the extreme com- 

 parative shortness of the alternate lamellae in the transverse sec- 

 tion, and the peculiar character of the broad, simple, cup-like 

 plates of the inner zone in the rough transverse fracture. 



Very common in the carboniferous limestone of Tullyard, 

 Armagh, Ireland. 



[Col. University of Cambridge.) 



[To be continued.] 



11.— Note on the Colour of a Freshwater Loch. By George 

 Dickie^ M.D., Lecturer on Zoology and Botany in the Uni- 

 versity and King^s College of Aberdeen*. 



Various vegetable productions have on different occasions been 

 recorded as having appeared in such profusion that they com- 

 municated a colour of greater or less intensity to bodies of fresh 

 water in which they naturally live. The plants in question be- 

 long to the Oscillatoriea and Nostochinece ; among the former, 

 Oscillatoria cerugescens has been recorded by Dr. Drummond 

 (Ann, Nat. Hist. vol. i. 1st Series) as giving a tinge to the water 

 of Glaslough in Ireland f ; I have found the same species at 

 Aberdeen, and particularly abundant in a small and shallow ar- 

 tificial lake, in sheets of great extent at the bottom. I have not 

 observed it, as stated by Dr. Drummond, "broken into innu- 

 merable fragments, and suspended like cloudy flocculi in the 

 water ;'' it sometimes however becomes detached from the bot- 

 tom and forms large masses on the surface. The following 

 plants belonging to the Nostochineae have been described by 

 Mr. Thompson of Belfast as producing the same effect : the 

 Anabaina spiralis {Spirillum Thompsoni, Hass.) was observed to 

 colour Ballydrain Lake in the county of Antrim ; Anabaina Flos- 

 aquce, Bory, he saw "tinging with its delicate green hue the 

 margin of the smallest of the Lochs Maben in Dumfries-shire,'^ 

 and Aphanizomenon incurvum, Morren, was " observed on the sur- 

 face of sheltered creeks in Ballydrain Lake.'' 



* Read before the Botanical Society of Edinburgh, Nov. 9, 1848. 

 •j* Oscillatoria ruhescens has been observed to communicate a red tint to 

 Lake Morat in Switzerland. 



