Mr. J. Ralfs on the Nostochinese. 339 



numerous, very minute. Vesicular cells oval. Sporangia (two 

 to eight in each chain) at first similar to the ordinary cells, but 

 usually less orbicular ; finally they become more or less oval, the 

 shorter ones approaching to orbicular, and the longer ones to 

 oblong j they are frequently but little broader than the vesicular 

 cell ; in fact their size never differs so much as in many species. 



Cylindrospermum catenatum differs from every other species in 

 its numerous sporangia. 



Cylindrospermum contains many other species, several of them 

 by no means uncommon in this country; but their descriptions 

 must be deferred to some future period, as my friend Mr.Thwaites, 

 who had paid great attention to them, was prevented by his ap- 

 pointment at Ceylon from fulfilling his kind promise to describe 

 them for this paper. 



Plate VIII. fig. 14. a, immature filament; b, mature state. 



Aphanizomenon, Morren. 



Filaments simple, flaccid, obsoletely jointed, " cohering laterally 

 into flat lamellae," aggregated into a mucous stratum ; vesicular 

 cells none ; sporangia linear, interstitial. 

 (Aphanizomenon, Morren. Limnochlide, Kiitz.) 



Aphanizomenon forms a thin, tender, mucous stratum of a 

 bluish colour. The filaments are extremely slender, flaccid, and 

 very obscurely jointed. No vesicular cells have been detected. 

 The sporangia are much elongated, either scattered or, more 

 usually, solitary near the centre of the filament. 



I have examined an authentic specimen of Limnochlide Flos- 

 aqiue, and as there seems to be no essential difference between 

 Aphanizomenon and Limnochlide I have united them, retaining 

 the former appellation on account of its priority. The filaments 

 in both genera are described as cohering in flat lamellse, but that 

 character is sometimes so little obvious in dried specimens, that 

 I am not inclined to place much dependence upon it as a generic 

 distinction, especially as I could not detect it in recent specimens 

 of a plant, presently to be described, which I think should by no 

 means be placed in a different genus. 



Authors differ widely respecting the proper situation of this 

 genus. In Harvey's ' Manual of British Algae ' it is placed at 

 the end of the Confervea, Montagne appends it to the Oscilla- 

 toriece, Endlicher omits it altogether, and Kutzing instituted for 

 it a distinct family, which he placed between Leptotrichece and 

 Nostochinece. Mr. Hassall, I believe, first placed it in this family, 

 and I fully concur with his observation that * the true position 

 of the genus is undoubtedly amongst the Nostochinece, connecting 

 them with the Oscillatoriece." 



22* 



