SUMMARY. 



With regard to the systematic arrangement of the Diatoms 

 found in Danish waters, I have in the main division followed 

 ScHtJTT (Engler og Prantl, "Die natiirlichen Pflanzenfamilien," 1. 

 Teil, 1. Abteilung G, pp. 55 — 57); although I do not think that the 

 term "Centricæ" can be appropriately used in contrast with "Pen- 

 natae." For if, by a centre of a Diatom, is understood that point 

 around which the different parts of the cell are symmetrically ar- 

 ranged, then — with the exception of the unsymmetricai forms — 

 all Diatoms have a centre — a Finnularia as truly as a Coscinodiscus. 

 But if the centre of a body is defined as a point from which any 

 straight line to the surface of the body is equal and opposite to 

 some other such line, then no Diatom has a centre, because the 

 epitheca is always larger than the hypotheca. In the more detailed 

 arrangement of genera under Centricæ I have followed Schutt. 

 I have divided Pennatæ into those with a raphe — Rhaphideæ, — 

 and those without a raphe — Arraphideæ. 1 agree with van Hecrck 

 in dividing the Raphideæ into Enraphidées and Celoraphidées, 

 only, as the first part of the latter word is French I prefer to 

 frame an entirely Greek term, Kryptoraphideæ. I did not venture 

 to use the term Ej'yptoraphideæ, although this term has nearly 

 the same meaning as Kalyptoraphideæ, because it had previously 

 been used in quite a differentmanner, i. e. to designate the "Centric" 

 Diatoms. 



Again, while dividing the group Enraphideæ similarly to van 

 Hecrck, I have altered his "Biraphidées" to Diraphideæ, and his 

 "Uiiiraphidées" to Monoraphideæ. ^ 



The late Mr. H. van Heørck informed me, in a letter written Jan. 1, 

 1909, that he had grouped the Euraphidées into the Biraphidées 

 and the Dniraphidées and established the group Celoraphidées, and 

 he has used these terms in his paper on the Diatoms of the. 

 "Belgica'" Eccpedition in "Resultats du Voyage du S. Y. Belgica". 

 Jiapports scientifiques & Botanique, Anvers, 1909. 



