27() f- H. OSTKMKI.I). 



lo ;i(l(l. Oiily oiK' iR'w c';isi' ol' micTospoii' roiinalion has been dis- 

 covered since Karsten's paper, viz. tlie microspore formation in 

 Chivt. Lorenzianum Griin. found i)y J. Schii.lku (Ber. Deutscli. Bol. Ges., 

 XXVII, iyi)9, p. 302) in the Gulf of Triesl. The formation described 

 corresponds rather \vell lo the manner of sporulation found by Gran 

 in Chœt. decipiens and by George Murray (Proc. Roy. Soc. Edin- 

 burgh, XXI, 1896, p. 207) in Chœt. boréale; as to the hypothesis ad- 

 vanced by the author on the cause of the rarity of microspores — 

 viz.. that the microspore formation in most species should take 

 place by the germination of the resting cysts -, I have onl}^ lo say 

 that it is a purely Iheorelical supposition, for which we have no 

 basis as long as we do not know a single case of germination of a 

 resting spore. It is a very remarkable fact that in spite of the nu- 

 merous studies on the plankton diatoms during the last two decen- 

 nia, nothing has been discovered with regard to this important mat- 

 ter. It is to be hoped that we may soon get this mystery solved. 



I) ist lib. Oceanic species of a northern character, a dominant species 

 over wide areas of the Xortli .\tlantic and its tritiutaries. 



25. Chaetoceras diadema (Ehrbg.j Gran, Norske Nordhavs Exp., 

 Protophyta, 1897, p. 20, pi. 2, figs. 16— 18; Nord. Plankton XIX, p. 84; 

 C. (jroenlandiciim Cleve, Bih. K. Svenska Vet. Akad. Handl., Bd. 22, 

 afd. 2, No. 4, 1896, p. 7, pi. 2, figs. 3—5; Syndcndrium diadema Ehrbg. 

 Mikrogeologie, pi. 35, A, XVllI, 13. 



Found sparingly in one sample (Aug. 1906) in the pack-ice, 

 rather sparingly in some samples from the coastal water (July 1908) 

 and not uncommon in samples from Danmarks Havn in August — 

 September 1907 and here with resting spores. 



Di strib. Northern neritic species of wide distribution. 



26. Chaetoceras Wighami Brightw., Quart. Journ. Microsc. 

 Science, IV, 1856, p. 108, pi. 7, figs. 19—36; Gran, Nord. Plankton, XIX, 

 1905, p. 88; Ostenfeld, Wiss. Ergebn. Aralsee-Exp., Lief. VIII, St. Peters- 

 burg, 1908, p. 153, pi. 5, figs. 9 — 12; C. bottniciim Cleve in Aurivillius, 

 Bih. K. Svenska Vet. Akad. Handl., Bd. 21, afd. 4, No. 8, 1896, p. 14, pi. 1. 



Found rather sparingly in Aug.— Septm. 1907 in Danmarks Havn; 

 rather often occurring in the coastal water in July 1908 and here 

 common in a few samples; further single chains found in a sample 

 from the pack-ice (July 1908). 



Distrib. Eurjhaline neritic species, known from the coasts of Europe 

 and Arctic countries, furtlier from the Caspian and Aral Seas. 



27. Chaetoceras debile Cleve, Bih. K. Svenska Vet. Akad. Handl., 

 Bd. 20, afd. 3, No. 2, 1894, p. 13, pi. 1, fig. 2; Østrup, Medd. om Grøn- 



