FRESHWATER ALQM. 31 



39. Phormidium tenue. 

 Phormidium tenue (Menegh.) Gom., torn, cit., p. 169, PI. IV., figs. 23-25. 



Diam. fil. = 1 ' 5-2 fi. 



Hah. — Freshwatei- pond in ice off Black Island, McMurdo Strait, December 31st, 

 1902 (forming a thin stratum overgrown by Nodidaria koettlitzi and species of 

 Oscillator ia) ; Gap pond, Winter Harbour, December 15tli, 1903. 



The cell-contents were occasionally slightly granular. 



40. Phormidium fragile. 



Phormidium fragile (Menegh.) Gom., torn, cit., pp. 163-164, PL IV., figs. 13-15. 



Diam. trich. = 1 ■ 5-1 ' 8 jU, ; long. cell. = 1 * 5-2 {j.. 



Hah. — Freshwater pond in eskers upon ice, half-way between Black and 

 Brown Islands, January 3rd, 1903; Gap pond. Winter Harbour; growing in and 

 through ice in pond among the eskers which border the shore of the Western mainland, 

 December 2nd, 1902. 



41. Phormidium frigidum sp. n. 



(PI. I., fig. 52.) 



Strato, ut videtur, tenui, membranaceo, colore ? (ut videtur serugineo) ; filis 

 plerumque plus minusve tortuosis et intricatis, interdum parallelis ; vaginis mucosis, 

 in muco hyalino diffluentibus ; trichomatibus inter cellulas distincte constrictis, ssepe 

 fere moniliformibus, apice non attenuate, cellula apicali rotundata ; cellulis tarn longis 

 quam latis vel ad duplo longioribus, cytoplasmate dilute serugineo, homogeneo, rare 

 granulato ; dissepimentis plerumque cum granulo magno distincto ssepe deplanato in 

 utraque parte, interdum modo in altera parte, vel sine granulis ; calyptra nulla. 



Diam. trich. = ' 8-1 • 2 /x, (interdum ad 1 • 5 /a). 



Hah. — Dull brick-coloured ice, situated in long level line, as though in situation 

 of former water-level, four feet above frozen water-course through "Penknife ice," 

 McMurdo Bay, September 13th, 1902. 



This form, which presumably grows on the surface of the ice, was only present 

 in minute pieces, so that the general colour of the stratum cannot definitely be stated. 

 It belongs to Gomont's first section Moniliformia, but diff"ers from all other species of 

 that section in the frequent presence of granules at the dissepiments ; although 

 occasionally wanting, the granules were always present on the majority of the septa in 

 each filament. The granules were generally more or less flattened against the 

 dissepiments, which gives the trichomes a rather characteristic aspect {cf. the uppermost 

 filament in fig. 52). 



Except for the shortness of the cells and the granulated dissepiments the species 

 resembles P. angustissimum W. and G. S. West. It also comes close to P. fragile 



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