NOSTOCER, 235 
Professor Wittrock suggests that the genus Anabaena should be 
divided into four sab-genera, under the following designations :— 
Sus-Gen. 1. Trichormus. Spores globose, or subglobose, hetero- 
cysts intercalated, distant from the spores. 
Sus-Gen. 2. Dolichospermum., Spores subellipsoid or sub- 
cylindrical, heterocysts as in Trichormus. 
Sus-Gen. 3. Spherozyga. Spores subellipsoid or subcylindrical, 
heterocysts intercalated, proximate to the spores. 
Sus-Gen. 4, Cylindrospermum. Spores subellipsoid or cylindrical, 
heterocysts for the most part terminal and proximate to the spores. 
Anabaena flos-aque. Kutz. Tab. Phyc.1., t. 94. 
Free swimming, membranaceous, blue-green. Trichomes more 
or less curved, often circinate, joints spherical, or from mutual 
pressure elliptic or quadrate. Heterocysts intercalated, elliptical. 
Spores globose. 
Sizz. Cells :0045-006 mm; heterocysts -012--014 mm. 
long; spores ‘008-'01 mm. 
Rabh. Alg. Eur. ii., 182. Kirch. Alg. Schl, 235. 
Nostoc flos aque, Lyngb. Hydro. t. 68, f. D. 
Trichormus incurvus, Allm, Ann. Nat, Hist, xi., 168. 
var. circinalis. Kirch. Alg. Schl. 235, 
Trichomes more circinate, and joints rather larger. 
Sizz. Cells (007-01 mm. ; spores -012-:014 mm, diam. 
Anabaena circinalis, Rabh. Alg. Eur, ii., 183. 
Anabaena spiralis, Thompson Ann, Nat. Hist. (1846) v., 
p. 81. 
Trichormus spiralis, Ralfs Ann Nat. Hist. (1850) p. 328. 
In ponds, moor pools, &c. : 
Plate XCIII. fig. 1. Trichomes X 400 diam.; b Trichormus spiralis 
after Ralfs ; c var. circinalis, trichomes x 400. 
From the description and figure given by Ralfs, under the name of 
Trichormus spiralis, we have no doubt that Thompson’s Alga, which 
himself termed Anabaena spiralis, was the variety circinalis of this 
species, although Hassall’s figure and interpretation is entirely different. 
The account which Thompson gives of his ‘ Alga which colours Bally- 
drain Lake,” is as follows :— 
“On visiting the lake (July 15) to-day I found that the whole body of 
water was tinged with a dull faintly glaucous hue. On going out in a 
boat to ascertain the cause of this appearance, I saw that the water was 
everywhere filled with extremely minute particles, which might be com- 
pared to the motes in a sunbeam. To the unassisted eye they seemed 
as delicate as the finest human hair, and of a spiral form. On enquiry 
I learned that the appearance had been observed only for the last four 
or five years, and for about three months in each year. One of my 
friends had looked upon its approach with dread, as it interfered so 
much with his angling, that during the period of its continuance this 
spot had to be abandoned.” Subsequently the plant was observed as 
2. 
