276 С. H. OSTENKELl). 



to add. Only one new case of microspore formation has been dis- 

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

 Chœt. Lorenziamim Grun. found by J. Schiller (Ber, Deutsch. Bot. Ges., 

 XXVII, 1909, p. 352) in the Gulf of Triest. The formation described 

 corresponds rather well to 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 only to say 

 that it is a purely theoretical 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) i strib. Oceanic species of a northern character, a dominant species 

 over wide areas of the North Atlantic and its tributaries. 



25. Chætoceras diadema (Ehrbg.) Gran, Norske Nordhavs Exp., 

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

 С groenlandicum Cleve, Bih. K. Svenska Vet. Akad. Handl., Bd. 22, 

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

 Mikrogeologie, pi. 35, A, XVIII, 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. 



Distrib. Northern neritic species of wide distribution. 



26. Chætoceras 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. bottnicum 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. Euryhaline neritic species, known from the coasts of Euroije 

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



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

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



