BY G. I. PLAYFAIR. 353 



puncta-spot. In neither of these samples were the filaments in 

 the Phormiditim-condition. 



Phormidium corium (Ag ) Gomont. (PI. xlvi, f.7.) 



Trich. diam. 3-3J; cell. alt. 3-8, vulgo 4 /x. 



Lismore(205, 209). 



Cf. Gomont, I.e., p.172, PI. v., f.l, 2. Pale blue, generally 

 transparent, with distinct dissepiments, protoplasm minutely 

 granulate, sometimes a central body in the middle of each cell. 

 Stratum membranous or coriaceous. 



Var. ACUMINATUM, n.var. (PI. xlvi., f.8.) 



Formse typicae consimile sed latius, Trichomata dilute viridia 

 apicibus acute conicis. 



Trich. diam 5-8; cell. alt. 3-8, apical. 8-10 /x. 



Lismore (207, 211,228). 



First obtained from a roadside ditch near the Cathedral. 

 Gomont gives diam. 3-4| /x for the type, cell. alt. 3-8 /x. Our 

 specimens agree exactly with his details. In this form, the 

 trichomes are green rather than blue, and the natural tips are 

 acutely conical, in broken filaments (with projecting sheath) 

 they may vary from simply rounded to bluntly conical Phorm. 

 Crouani Gomont, I.e., p. 175, is a still broader form of this species, 

 diam. 7J-10J, cell. alt. 4-8 /x; the description agrees perfectly with 

 that of Ph. co7-iu7n, and var. acuminatum just connects the two 

 sizes. I do not see how PA. papyraceum{Ag.) Gomont, Ic , p. 173, 

 PI. V , f.3, 4, can be distinguished from Ph corium. 

 Var. CONSTRICTUM, n.var. (PI xlvi., f.9.) 



Trichomata dilutissime aeruginosa, ad genicula constricta, 

 apicibus naturalibus acutissime conicis ; cellulis cylindraceis, 

 diametro ad duplum longioribus, protoplasmate minute granulato. 



Trich. diam. 4-5; cell. alt. 8 /x. 



Lismore (228). Cum priori. 



Trichomes about the size of the type, but distinctly constricted 

 at the joints, and very sharply pointed; the cells cylindrical, not 

 quadrate as usual in this species. All the forms of Ph. corium 

 were true Phormidia, the stratum membranous, sheaths agglu- 

 tinated. 



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