FEESHWATEK ALG^. 37 



granuloso ; trichomatibus gradatim attenuatis, sed non in pilum productis, non 

 pseudo-ramosis, inter cellulas vix constrictis, dissepimentis distinctis ; cellulis ad 

 basin trichomatis tarn longis quam latis vel modice deplanatis, sursum diametro ad 

 duplo longioribus, contentu serugineo granuloso. 



Diana, fil. ad bas. = 8-9 /x, ; diam. trich. ad bas. = 5-6 /u. ; diam. trich. in media 

 parte = 4-5 ju, ; diam. heterocyst. = 5-6 ju ; crass, parietis vaginae = • 8 /x. 



Hob. — Gap pond, Winter Harbour. 



The filaments are curved and intertwined to such an extent as to make it almost 

 impossible to follow one from end to end. (fig. 158). In places these densely 

 entangled filaments form a thin stratum completely hiding the underlying Phormidium, 

 but at other points they are much more loosely arranged. The base of the sheath is 

 often a little inflated, and in this case there is a rapid narrowing of the filament just 

 above the base ; beyond that point, however, the attenuation is very gradual, and the 

 termination of the filament is only slightly narrower than it is just above the inflated 

 base (figs. 159, IGO). The terminal cell of the trichome appears to be more or less 

 pointed and acute (figs. 159, 160). 



This species bears considerable resemblance to the Calothrix . s^p., described and 

 figured by Messrs. West (op. cit., p. 298, PL XXV., figs. 55-57), which they regard as 

 probably being a new species of the genus ; but there are some important diff'erences — 

 viz. the subtorulose cells (which are quite diff"erent to those of C. intricata), and the 

 obtuse terminal cell of the trichomes. Possibly Messrs. West's specimens are a variety 

 of C. intricata. The genus Calothrix is, however, evidently well represented in the 

 Antarctic with a considerable number of new forms. 



There is some resemblance between C. intricata and C. epij)hytica W. and 

 G. S. West, but, apart from the somewhat larger dimensions, the former diff'ers in 

 the fact that the trichomes do not taper into a hair and in the highly tortuous 

 character of the filaments. 



56. Calotheix gracilis, sp. n. 

 (PI. Ill, figs. 164-172.) 

 Fills rectis vel saepe modice flexuosis, solitariis vel subgregariis, usque ad 400 yx 

 longis, in superficie Phormidii repentibus, rare pseudo-ramosis ; vaginis tenuissimis, 

 hyalinis, arctis, basin interdum inflatis ; heterocystis basilaribus, et in fills longioribus 

 etiam intercalaribus, plerumque solitariis, in vaginis inclusis, deplanatis, hemisphsericis 

 vel rarius obconicis, membrana modice incrassata contentu homogeneo ; trichomatibus 

 non in pilum productis, plerumque gradatim attenuatis, sed ubi basis 'vaginae inflata est 

 subito attenuatis paulum supra basim, cellula apicali acuta ; trichomatibus in parte 

 basali inter cellulas modice constrictis ; cellulis inferne ssepe paulo deplanatis 

 (prsesertim ubi basis fili inflata est), in media parte et superne diametro circa l^plo 

 longioribus, contentu cum paucis granulis ; sporis (an maturis ?) binis (semper ?), 

 cylindricis, diametro l5-2plo longioribus, membrana levi. 



