206 



DUBLIN NATITRAL HISTOIIT SOCIETY. 



in a succinct manner, the views put forward above, as well as the end 

 sought to be accomplished in the present paper by the institution of the 

 genus. 



'Frond lenticular, as long as or longer than 



broad; segments usually semi-orbicular, 



five or rarely three-lobed (with three, or 



rarely two subdivisions, «, I, c, or a^b, c) ; 



lobes radiant, incised or dentate, rarely 



only sinuate, widening outwards ; central 



constriction usually linear. Micrasterias. 



{Vide "Brit. Desmidiae," p. 68, etseq.) 



Frond longer than broad ; segments more or 



less conical, five or three-lobed, orsinuated 



(with three or two subdivisions, either 



a, h, c, or a'~"h, c, or ah, c, or rarely ah'^c), 



J possessing variously disposed, circular, in- 



Frond simple, compres- 

 sed, deeply constricted, 

 segments lobed or si- 

 nuate (Schizomerous); 

 lobes either incised, 

 sinuate, or entire. 



flated prominences; ends emarginate, or 

 rarely with merely a concavity; central 

 constriction linear. JEuastrum. 



( Vide ''Brit. Desmidiae," p. 78, et seq.) 

 Frond about as long as or longer than broad ; 

 segments three-lobed (with two subdivi- 

 visions al, c,), without inflated promi- 

 nences ; basal lobes horizontal, attenuated 

 outwards, end lobe expanded laterally, its 

 lateral projections parallel in direction with 

 the basal lobes ; ends straight or rounded, 

 entire; central constriction forming an 

 acute -angled spreading notch : — 



Tetrachastrum, 



Frond longer than broad ; segments constricted about two-thirds of the 

 way from the base ; lobes mucronate, their extremities not bidentate. 



mucronatum. 



Frond as broad as or slightly broader than long ; segments constricted 

 about half-way from the base ; lobes not mucronate, their extremities 

 bidentate. 



Fron d with convex ends ; lobes conical ; colour rich green, oscitans. 



Frond with straight ends, plane ; lobes triangular ; colour pale. 



pinnatifidum. 



Mr. Sanders having expressed the pleasure he had experienced in 

 listening to the foregoing paper, proposed a vote of thanks to the Rev. 

 E. V. Dixon for his interesting communication, which was seconded by 

 Mr. Archer, and passed unanimously. 



