46 ARKIV FÖR BOTANIK. BAND H. N:0 9. 



Achnanthes sejitata, since the valve, drawn by Cleve in fig. 

 22 b (D. Arct. Sea, Tab. 4), belongs to the latter species. 

 Both of the species in question occurring rather abundantly 

 in the Knjäsha-samples, I have been able to compare them 

 closely in valvar view, and state their difference, which may 

 be seen when comparing the figures 55 — 57 of this paper. 



Later on, Cleve has united Achn. arctica with Achnanthes 

 suhsessilis KOtz., in which I cannot agree with him. These 

 forms are certainly quite different in general structure, habi- 

 tually, and in size. The numbers of 30 — 50 jj. for the length 

 and 10 — 11 ]x for the breadth, given in Cleve's Synopsis for 

 Achnanthes brevipes var. intermedia, apply to the true Ach- 

 nanthes suhsessilis, but not to the considerably larger Ach- 

 nanthes arctica, for which Cleve himself in his original de- 

 scription states a length of 48 [J-, which to judge from the 

 figure must be a misprint for 96 a or more, a heigth of 24 ^. 

 and a breadth of 17 [a (as in my form). In Mar. d. 0st- 

 Gronl., p. 408, 0strup follows Cleve in uniting the two 

 different forms Achnanthes suhsessilis and Achnanthes arc- 

 tica; moreover he has not remarked the complexity of the 

 latter, sensu Clevei, and figures as »Achnanthes suhsessilis var. 

 incurvata» a constricted form of Achn. septata. 



Only for the case that Achnanthes arctica be a sporangial 

 form, it could possibly be the same species as Achn. septata. 



Achnanthes septata n. sp. — PL 2, f. 57 a, b. — Syn. 

 Achnanthidium arcticum Gl. p. p. D. Arct. Sea, Tab. 4, f. 22 b. 



Frustule linear, genuflexed, with subcuneate, obtuse ends 

 and broad, distinct diaphragms at the ends. Length of the 

 valves 70 — 100 [j., breadth 14 — 17 [x. Lower valve with an 

 indistinct axial area and no areas at the ends. Central area 

 a narrow, transverse fascia; central pores approximate. Striae 

 subradiate, 6 in 10 {J-, composed of coarse, quadrate puncta, 

 forming straight longitudinal rows. Upper valve unknown. 



Foss. : Kk. Knjäsha, rather frequent. 



Distr. {mar.): West and East Arctic Sea. 



The diaphragms at the ends of the valves are a feature 

 common to this species and to Achnanthes groenlandica Cl. In 

 other respects, they, however, are different enough; in size 

 f. i., the latter being a smaller and more gracile form, only 

 5 — 7 'J. in breadth. Moreover, the central pores are not distant 

 from each other in Achn. septata, as is the case in Achn. 



