20 Dr. Dickie on the Colour of a Freshwater Loch. 



tion, 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.] 



II. — 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 Oscillatoriece and NostochmetB ; among the former, 

 Oscillatoria arugescens 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 NostochinecB have been described by 

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

 Anabaina spiralis [Sjnrillum Thomjjsoni, 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 tbe Botanical Society of Edinburgh, Nov. 9, 1848. 

 t Oscillatoria riibescens has been observed to comnuinicate a red tint to 

 Lake Morat in Switzerland. 



