Mr. J. Ralfs on the Nostochinese. 



night, rays an inch or more in length. Filaments elongated, 

 comparatively stout, visible to the naked eye, under the lens full 

 green when grouped, but bluish green when scattered. Ordi- 

 nary joints orbicular. Vesicular cells elliptic, broader than the 

 ordinary ones. Sporangia near the middle of each series of 

 ordinary joints, most frequently solitary, rarely more than two 

 together, at first oval, afterwards oblong, finally cylindrical, and 

 about six times longer than broad. In their early state they 

 resemble the vesicular cells in form ; but the presence of granular 

 matter and the absence of junction-globules reveal their true 

 character : the longer ones are frequently contracted at the mid- 

 dle, a circumstance I have occasionally noticed in those species 

 which have elongated sporangia. 



Dolichospermum Ralfsii is distinguished from D. inaquale by 

 its elliptic vesicular cells (which are comparatively less broad), by 

 its more orbicular ordinary joints and by having fewer sporangia. 



Plate IX. fig. 2. 



3. D. Thompsoni ( ). Filaments spirally curved; ordinary and 



vesicular cells spherical ; sporangia oblong, curved, usually solitary. 

 Anabaina Flos-aquce, Harvey, Manual of Brit. Algae, p. 186 (1841) ; 

 Hassall, British Freshwater Algse, p. 282. t. 75. fig. 2. 



" Floating like powdered verdigris on one of the small Lochs Ma- 

 ben, Dumfries-shire," Mr. W. Thompson. 



A specimen of this plant, given me by Mr. Thompson, forms 

 on paper a thin stain of a bluish green colour. Filaments mo- 

 niliform and loosely spiral. Ordinary and vesicular cells orbi- 

 cular, and so much alike in form and size that in the dried state 

 I am unable, with absolute certainty, to distinguish the latter 

 from ordinary cells which have lost their granular matter. Mr. 

 Thwaites however informs me, that by a careful adjustment of 

 the lens, he has detected the puncta in the vesicular cell, in which 

 also he finds the membrane firmer than in the others. Sporangia 

 solitary (rarely two together) in each series, two or three times 

 longer than broad, curved, so as to appear somewhat reniform, 

 and more rounded at their ends than is usual in this genus. 



This species is easily distinguished from the others by its 

 curved filament and reniform sporangia. Its moniliform, spiral 

 filament agrees better with Trichormus than with Dolichospermum, 

 but in its elongated sporangia it differs from every species of the 

 former. 



Plate IX. fig. 3. 



4. D. Smithii* (Thwaites MS.). Filaments straight, each included in 



* For the description of this and the following species I am indebted to 

 Mr. Thwaites. 



