Fresh- water Algm, &c. By A. W. Bennett. ~ 11 



OSCILLAEIACE^. 



Oscillaria tenuis Ag. 



* „ tenerrima Ktz. Bog pool, Eoclie. 



* „ muscorum Carm. Bog pool, St. Denis. 



* Oscillaria i)rince'psN-aMG]i. Fig. 4. 



Filaments free-swimming, quite solitary, 30-38 fi broad without the 

 slieath, about 44 fx including the sheath, 20-40 times as long as broad. 

 Invested in a very thin mucous sheath, fitting closely to the filament, 

 and sometimes projecting slightly beyond it where broken. The filament 

 is somewhat suddenly narrowed at both ends to a tapering extremity, 

 which bends downwards ; otherwise it is quite straight. Endochrome 

 a very bright blue-green, obscurely divided into pseudo-cells about three 

 times as broad as long, much narrower in the curved ends ; it shows 

 here and there indications of breaking up into the " cellulae perdurantes " 

 described as specially characteristic of the genus Lynghya. 



This fine species was seen several times in bog pools ; the filaments 

 always moving backwards and forwards with a slow horizontal motion. 

 It might readily, at first sight, be mistaken for a Desmidium, which it 

 resembles in form and size. The thin mucous sheath, and the tendency 

 of the contents of the filament to break up into resting-cells, seem to 

 indicate an affinity with Lynghya; but the form of the extremities 

 of the filaments is altogether that of an Oscillaria. I have some doubt 

 in identifying it with Yaucher's species, which is described by Eabenhorst 

 as forming a mucous stratum, while this was observed by me only in 

 rare soHtary filaments. On the whole, however, it seems to agree with 

 this species, though it also shows considerable resemblance in size, and 

 in its solitary filaments, to 0. percursa Ktz. 0. imijerator Wood I take 

 to be identical. 



The genus Oscillaria is at present very poorly represented in the 

 British flora. Dr. Cooke includes only twenty species in his ' British 

 Fresh- water Algse ; while Eabenhorst, in his ' Flora Europaea Algarum,' 

 enumerates no less than sixty-four, many of them, however, of only 

 very doubtful value. The larger species in particular are conspicuously 

 absent from our flora ; and the addition of this, perhaps the most striking 

 of all, is therefore of some interest. 



Lynghya ochracea Thur. 

 *Spirulina oscillarioides Turp. Bog pool, Eoche. 



SlKOSIPHONILS!. 



*Stigonema minutum Hass. ? Figs. 5-10, 



Whether this species is correctly named I am very uncertain. 

 Isolated fragments were observed several times, intermixed with other 

 floating algae, on a bog pool at Mawgan. The main filament averages 

 about 40 yu, in thickness ; from this proceed branches on one side only, 

 frequently in pairs, these again branching copiously; the average 

 thickness of the branches is about 25 /i. There was no indication of a 

 mucous sheath. The branches contain a single row of elliptical pseudo- 

 cells, the broader axis at right angles to the direction of the filament ; 



