238 NEMATOGEtt^E. 



" Immediately distinguishable from its congeners on account of its 

 possessing a definite gelatinous sheath to each of its filaments, which 

 are of smaller diameter than those of any other species of Dolicliosper- 

 mum. The ordinary cells are subspherical, somewhat compressed, and 

 of less diameter than the heterocysts, which are barrel-shaped, and 

 with very distinct puncta. The numerous spores, which are about twice 

 the diameter of the ordinary cells, are elongated and cylindrical, very 

 variable in length and in the number which occur together, and their 

 ends are slightly truncate." Rolfs. 



Plate XCIII. fig. 7. Portions of trichomes with heterocysts and 

 spores X 400 ; fig. a from Scandinavian specimens ; fig. b from British 

 specimens. 



Anabaena oscillarioides. Bory. Diet. Hist. Nat. 



Forming a bluish green stratum. 



Trichomes elongated flexuous, joints subquadrate, distinct ; 

 heterocysts barrel-shaped or elliptic. Spores oval, catenate, 

 somewhat larger than the vegetative cells. 



SIZE. Cells -G04--005 x -004--006 mm. Heterocysts -006- 

 008 x -007--009 mm. Spores -007--008 X '008--012 mm. 

 (Wittrock.) 



Nord. & Wittr. Alg. Ex. No. 196. 



Sphcerozyga oscillarioides } Kutz. Sp. Alg., p. 291. Borzi. 

 Alg. Fico. 286. 



Trichormus oscillarioides, Kalfs in Ann. Nat. Hist. 1850, p. 

 329, t. 8, f. 5. 



In brackish ditches. 



" It differs from A. TTiivaitesii by its more quadrate ordinary cells, and 

 by its smooth and elliptical heterocysts." Ralfs. 



Plate XCIII. fig. 6. Portions of trichomes with spores and hetero- 

 cysts X 400. 



Anabaena Thwaitesii. (Ralfs.) 



Trichomes moniliform, straight or nearly so, joints quadrate. 

 Heterocysts oblong sub-quadrate, hardly exceeding the joints 

 in diameter. Spores numerous, cylindrical with truncate ends, 

 very variable in length. 



SIZE. Cells -006--007 mm. Heterocysts -008 x '01 mm. 

 Spores -01--012 X '025--03 mm. 



Dolichospenniim Thwaitesii^ Ralfs Ann. Nat. Hist. 1850, 

 337, t. 9, f. 5. 



In freshwater pools, and brackish ditches. 



Allied to A. Smitliii, but its filaments are not included in a definite 

 gelatinous sheath. Its filaments are also stouter, and there is a differ- 

 ence in the form of its cells. The heterocysts are quadrangular, and 

 hardly exceed in diameter the ordinary cells. The cylindrical truncated 

 spores are numerous, many in a chain, and variable in length, about 

 twice the diameter of ordinary cells. 



Plate XC11I. fig. 5. Portions of trichomes with heterocysts and 

 spores X 400. 



