20 Dr. Dickie on the Colour of a Freshwater Loch. 
tion, radiating lamelle forty-eight, 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 lamelle 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 bec aen: 
Armagh, Ireland. 
(Col. University of Cambridge.) 
[To be continued. } 
II.—Note on the Colour of a Freshwater Ticks By axoues 
Dicxiz, 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 Oscillatorice and Nostochinee ; among the former, 
Oscillatoria erugescens has been recorded by Dr. Drummond 
(Ann. Nat. Hist. vol. i. 1st Series) as giving a tinge to the water 
of Glaslough in Ireland}; 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 followimg 
plants belonging to the Nostochinee 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- 
aque, 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. 
+ Oscillatoria rubescens has been observed to communicate a red tint to 
Lake Morat in Switzerland. : 
