220 



E. Jargensen. 



rar. ventrieosa (Greg.) Cl. 

 Cl. 1. c. p. 135. Amphora v. Greg. Diat. of Clyde p. 511, pi. XII, f. 68. 



Not unfrequent, Moskenstrommen r, Stamsund r, the 0stnes- 

 fiord r +, Stene r, Gaukvsero +. 



Answers completely to Gregory's species, but is very variable. 



Distribution: Coasts of the North Sea. Sweden. Arctic 

 regions. The Mediterranean. Red Sea. 



Kpitlicmia Breb. 



E. turgida (Eheb.) Kutz. 

 Kutz. Bacill., pi. 5, f. 14. Van- Heurck Synops., pi. 31, figs. 1—2. Navieula 



t. Eheb. 1830. 



Fresh water species. 



Tar. Wester manni (Ehrb.) Grin. 



Grun. in Wien Verb. 1862. p. 325. Van Heokck Synops. p. 138, pi. 31, t 8. 



Navieula W. Ehrb. 1833. 



Very rare: Gaukvaero, r; Moskenstrommen, r. 

 Distribution: In brackish water. Coasts of the North Sea. 



E. argiis (Eheb.) Kit/. 



Kutz. Bacill. pi. 29, f. 55. Van Heueck Synops. pi. 31, figs. 15—17. Eunotia 



argus Ehrb., Mikrogeol. pi. XV A, f. 59. 



Very rare: Brettesnes — Skroven r, Gaukvaero r. 

 Distribution: Fresh water species; also in brackish water. 

 Frequent, especially in Northern Europe and in alpine localities. 



E. zebra (Ehrb.) Kutz. 



Kutz. Bacill. pi. 5, f. 12: pi. 30, i. 5. Van Heurck Synops. pi. 31, figs. 9, 

 11—14. Eunotia :. Eheb. Inf. p. 191, pi. 21, f. 19. 



Very rare: Gaukv:m> r, Stene r. 

 Distribution: Common fresh water species. 



E. musculus Kutz. 

 Kutz. Bacill. pi. 20. f. 6. Van Heurck Synops. pi. 32, figs. 14 — 15. 



rar. eonstricta (Breb.) V. H. 



Van Heurck Synops. p. 140: Traite d. Diat. p. 297, pi. 9, f. 360. Epithemia c. 



Breb. in W, Sm. Brit. Diat. I. p. 14, pi. 30, f. 248. 



Very rare: Svolvsr r, Gaukvaero r. 



Distribution: Coasts of the North Sea and Western Europe. 

 The Mediterranean. 



E. gibberiila Kutz. 

 Kutz. Bacill., pi. 30, f. 3. Van Heokck Traite d. Diat., p. 297, pi. 30, f. 825. 



Rare: Svolvaer, r. 



rar. produeta Gruk. 

 Van Heurck Synops. pi. 32, figs. 11 — 13. 



Rare: Stamsund, r. 



Distribution: Marine, also in brackish and fresh water (var, 

 produeta Gbun.), frequent in Europe and America. 



Rhopalodia gibba (Ehkb.) Otto Mull. 1895. 



Epithemia gibba Kutz. Bacill. p. 35, pi. 4, f. 22. Van Heurck Synops. p. 139i 



pi. 32, tigs. 1--2. 



var. ventrieosa (Kutz.) Grun. 



Grcn. in Wien Verb. 1862, p. 327. Epithemia reiitrirosn Kutz. Bacill. pi. 30, f. 9. 



Very rare: Gaukvaero, r; the Ostnesfiord, r. 

 Distribution: Common fresh water species. 



General remarks on the character of the bottom diatom flora. 



The most striking facts regarding the distribution of the dia- 

 toms in the foregoing list of bottom species are, that the arctic 

 forms are rare and that the flora, on the whole, has a much more 

 pronounced southern character than would be expected from the 

 geographical situation. This is in sharp contradistinction to the 

 character of the diatom flora during „the diatom inflow'' of plankton 

 species in spring (cf. above p. 88), when the actual arctic species 

 predominate. 



Generally speaking, the bottom flora shows a remarkable 

 agreement with that of the east coast of Scotland. It is especially 

 striking that a great many of the species described by Gregory in 

 Diatoms of the Clyde (1854) are common to these two regions, 

 situated at a rather considerable distance from each other. On the 

 other hand, these species also occur on the west coast of Norway, 

 at any rate most of them. It may, consequently, be concluded that 

 the characteristic western bottom flora of diatoms which inhabit 

 the coasts of the North Sea extend to the north as far as to past 

 the Vest-Fiord, probably, however, but little farther. 



For the sake of clearness, I divide the species found into (i 

 groups: 

 1. The actual arctic species, only found in the arctic region. 

 II. Species with a western and arctic distribution. 



III. Species with a very wide distribution, occurring from southern 

 regions right up into the arctic one. Some of these species 

 seem to be cosmopolitan. In Europe, the species belonging 

 to this group are generally found from the Mediterranean to 

 the arctic regions. 



IV. Western species, especially known from the coasts of the North 

 Sea. but not before mentioned from the arctic zone. 



V. Species with a southern and western distribution, generally 



occurring from the Mediterranean -- or still farther to the 



south — to the coasts of the North Sea. 

 VI. Species with only southern distribution, not before found so 



far north as on the coasts of the North Sea. 



Most of the species observed belong to group III, and many 

 of these species will probably later on be found to have a still wider 

 distribution than is at present known. For such more or less 

 decidedly cosmopolitan species, a thorough treatise on their varieties 

 and forms is a very important and valuable work, indispensable 

 when one wishes to obtain an accurate knowledge of the distribution 

 of identical and closely related species. Notwithstanding the exten- 

 sive material consisting of an immense number of facts and obser- 

 vations, often made with the utmost care and accuracy as to details 

 in structure, we are still obliged to acknowledge with regret that 

 our knowledge of the individual variations and real constancy of 

 the various distinguishing characters is very deficient. 



These species play an unimportant part with regard to the 

 character of the flora. It is. however, an interesting fact that, 

 apparently, so many species of diatoms are common to most seas 

 of the world. Even if a good many of these widely distributed 

 species, on a more thorough examination, should prove to consist of 

 similar, but separate species, having different areas of distribution, 

 there will still remain a great number of species which, in Europe, 

 occur from the Mediterranean to the Arctic Sea. It must, however, 

 be remembered that the valves of diatoms are almost of eternal 



