288 W. AND G. S. WEST 



This diatom was seen very sparingly, but the specimens were quite typical, and 

 agreed exactly both in the poles and the costae with those in A. Schmidt's Atlas Dial. 

 t. 23, f. 40. 



MYXOPHYCE7R 



NOSTOCACB2E 



Genus NOSTOC Vaucher 



46 Nostoc antarctica sp. n. (PI. XXV, Figs. 58-67) 



Thallo initio globoso, parvo, pallide eerugineo, demum irregulariter expanso, 

 fuscescente, tenuissimo et membranaceo, crispato, usque ad 4.5 cms. lato, brunneo ; 

 trichomatibus in thallo membranaceo densissime contorto-intricatis, confertissimis ; 

 cellulis parvis, globosis vel nonnunquam ellipsoideis, confertissimis tanquam paren- 

 chymaticis; heterocystis subglobosis, diametro trichomatis duplo latioribus, rare 

 solitariis sed plerumque 2-5 seriatis ; sporis ellipsoideo-globosis, episporio glabro. 



Diam. cell, veget. 2.5-3 M; diam. heterocyst. 6-7 M; diam. spor. 6.5-7 M. 



Hob. In ponds, Cape Royds. Also in ponds, Mt. Erebus. 



This is the most extraordinary Nostoc we have yet examined. Except for its 

 brown colour, the adult thallus presents all the appearance of a Monostroma. It is 

 exceedingly thin, with a crisped or pleated margin, and the trichomes are so densely 

 intricate as to give rise to an apparent parenchyma. In fact, we know of no species 

 of the genus with anything like this density of interlaced trichomes. The hetero- 

 cysts are rarely single, but more often 2-5 seriate, a character in common with 

 N. commune Vauch. 



N. antarcticum is perhaps nearest to N. minutum Desmaz. (vide Born, et Flah. 

 " Revis. Nostoch. Heter." Ann. Sci. Nat. 7 serie, Bot. vii, 1888, p. 209), from which 

 it differs in the much greater dimensions of the adult thallus, the much denser 

 disposition of the trichomes, the spherical cells, and the greater diameter and seriate 

 character of the heterocysts. 



NOTE. A species of Nostoc was observed from Blue Lake, forming rounded 

 colonies up to 800 M diameter. Diam. cells 4 M. The material was only fragmentary 

 and insufficient for accurate identification. 



OSCILLATORIACE^i 



Genus PLECTONEMA Thuret. 



47 Plectonema notatum Schmidle 



In Allg. lot. Zeitschr. 1901 Nos. 3 and 4, p. 4, Figs. 8, 9 on p. 2. 

 Crass, fil. 3-3.8 M, trich. 1.6-2 M. 

 Hob. In ponds, Mt. Erebus. 

 The specimens observed from the Antarctic were more in agreement with 



