330 Mr. J. Ralis on the Nostochinese. 



Stratum bluish green; filaments elongated, flexuose, monili- 

 form, often attenuated at the ends. Ordinary joints quadrate, 

 with rounded angles, frequently longer than broad, terminal ones 

 conical. Vesicular cells oblong, usually flattened at the ends so 

 as to appear barrel-shaped, broader than the ordinary joints, and, 

 according to Mr. Thwaites, always naked. Sporangia elliptic, 

 catenate, and somewhat larger than the ordinary cells. 



Trichormus oscillarioides differs from T. Thwaitesii by its more 

 quadrate ordinary cells and by its smooth and elliptic vesicular 

 cells. It may be known from T. recta by its elongated filaments 

 and by its more quadrate ordinary cells. 



Plate VIII. fig. 5. 



5. T. rectus* (Thw. MS.). Filaments bright green, straight, short, 

 slightly tapering towards the extremities ; ordinary cells subsphe- 

 rical, rather shorter than wide ; vesicular cells oblong, smooth, 

 scarcely wider than the ordinary cells, and never terminating the 

 filament ; sporangia spherical or oblong, numerous! 



Pools. Hanham, near Bristol, August 1847, G. H. K. Thwaites. 



This little species differs from every other we have seen in its 

 short, straight filaments, which are of a beautiful green colour. 

 The vesicular cells, of which there are seldom more than one or 

 two in each filament, are of a reddish colour, and about. half as 

 long again as wide. The ordinary cells are nearly spherical, 

 somewhat compressed, so as to be rather wider than long. The 

 sporangia vary in shape from spherical to oblong. 



Plate VIII. fig. 6. 



SphjErozyga, Ag. 



Filaments simple, generally moniliform, aggregated into a gela- 

 tinous stratum ; sporangia interstitial, in groups of two or 

 more connected by a vesicular cell. 



(Sphcerozyga, Agardh, Endlicher, Kutzing, Montagne. Ana- 

 baina, Bory, Brebisson.) 



Sphcerozyga agrees with Trichormus, Dolichospermum, Cylin- 

 drospermum, Aphanizomenon and Spermosira in its mode of growth 

 as well as in the colour and general appearance of its stratum, and 

 differs from those genera solely in the microscopic characters of 

 its filaments. 



The filaments are somewhat elongated. The joints, though 

 seldom so orbicular as in Trichormus, are usually very distinct. 

 The sporangia are generally elongated and cylindrical ; they oc- 

 cur in little groups of two or four, with a vesicular cell inter- 

 posed at the centre. Sometimes a vesicular cell has a sporangium 



* For the description of this species I am indebted to Mr. Thwaites. 



