236 NEMATOGEN.E. 



late as the 27th September, but on October 7th all had disappeared. In 

 the following year the Alga was seen first on the 3rd of July, and last 

 on the 23rd of September. 



" The specimens obtained were invariably of similar breadth, and 

 rarely presented more than four spiral turns, and when of this size were 

 l-50thof an inch in length. The species at first, when mingling with 

 the water, is of a dark green colour, when in calm weather it ascends to 

 the surface in separate particles it appears pale green ; when it does so 

 en masse (the earliest symptoms of decay) it is of a pale blue, and in the 

 last stage of decomposition ferruginous. When two of the spiral 

 portions come in contact they have an elastic power, by which they can, 

 though slowly, disentangle themselves, and separate from each other." 



Anabaena vaxiabilis. Kutz. Phyc. Gen, 



Gelatinous, submembranaceous, deep blue-green. Trichomes 

 slightly flexuously curved, almost parallel, verdigris green, joints 

 globose or elliptic, compressed or depressedly subcylindrical, 

 I-ITT times longer tban broad ; heterocysts intercalated, paler ; 

 spores numerous, seriate, ellipsoid, golden tawny, with a rather 

 thick membrane. 



SIZE. Cells -0035--004 mm. ; heterocysts '007 mm. ; spores 

 00801 x -012mm. 



Sphcerozyga Thwaitesii, Harv. Phyc. Britt. t. 113, B, 



Sphaerozyga variabilis, Kutz. Tab. Phyc. i., t. 96, Rabh. Alg. 

 Eur. ii., 193. 



Tricliormus rectus, Ralfs Ann. Nat. Hist. (1850) t. 8, f. 6. 



Anabaena licheniformis, Hass. Alg. 82, t. 75, f . 4 ? 



Trichormus Thwaitesii, Ralfs Ann. Nat. Hist. (1850) p. 

 329, t. 8, f. 4. 



In ditches. 



It forms thin gelatinous dark green patches either on the damp soil 

 covered at springtides, or at the bottom of brackish ditches and pools. 



Plate XCI2I. fig. 2. Trichomes X 400, with heterocysts and spores. 

 Anabaena Hassallii. Nord. and Wittr. Algce Exs. 



Trichomes equal, curved, often circinate, interwoven in a thin 

 blue-green stratum, joints globose or more or less compressed, 

 delicately granular ; heterocysts sphaerical, colourless, interca- 

 lated without order ; spores oblong cylindrical, single or in pairs, 

 distinctly curved, dark blue green, densely granulated, l^-2^ 

 times as long as broad. 



SIZE. Cells '008 mm. ; heterocysts 009-'01 mm. ; spores 

 012 x 025 mm. 



Sphcerozyga Hassallii, Rabh. Alg. Eur. ii., 195. 



Anabaena flos-aquce, Hass. Alg. 282, t. 75, f. 2, Harv. Man. 

 p. 186. 



Dolichospermum Thompsoni, Ann. Nat. Hist. (1850), t. 9, 

 f. 3. 



