A. CLEVE-EULER, DIAT. FLORA OF FINLAND. 45 



Achnanthes brevipes Ac. var. angustata Grev.? — Cleve, 

 Syn. Nav. D. II, p. 194. — Syn.? Achnanthes pennata Cl. 

 Vega-Exp. D. Tab. 35, f. 2. — Icon. nost. PI. 2, f. 54. 



Foss.: Kk. Knjäsha, rare. 



The specimen, drawn in fig. 54, agrees well with Cleve's 

 Achnanthes pennata in size and outline. Only it has distinctly 

 punctate striae, the puncta forming straight transversal as 

 well as longitudinal rows, 10 in 10 {x, whereas Cleve's figure 

 has been delineated with smooth striae. As the Synopsis 

 (II, p. 194) does not tell anything about the nature of the 

 striae, the identification of my form with Achn. pennata is 

 not perfectly certain. It is, however, probable that all true 

 forms of Achnanthes brevipes have punctate striae, thus also 

 the latter variety. 



Achnanthes arctica (Gl.) Achnanthidium arcticum Gl. p.p. 

 D. Arct. Sea, p. 25, Tab. 4, f. 22 a (not b). Achnanthes brevipes 

 Ag. var. intermedia Kütz. Cleve, Syn. Nav. D. II, p. 193 

 p. p. — Icon. nost. PI. 2, f. 55 a, b, 56. 



Frustule almost cylindrical, genuflexed, with broad, 

 rounded ends, very slightly contracted in the middle, CO — 

 100 \i in length, 17 [i in breadth. Upper valve with 6 — 7 

 rows of coarse, subquadrate, distant alveoli in 10 [j.; in each 

 row 5 alveoli in 10 [j.. Alveoli forming somewhat undulating 

 longitudinal rows. Axial area distinct or not. Lower valve 

 with rather distant median pores and a linear axial area, 

 dilated in the middle to a somewhat broad, transverse fascia 

 and near the ends to small rounded areas. Striae subradiate, 

 8 in 10 [J., coarsely punctate. Puncta quadrate, forming re- 

 gular longitudinal rows. 



The frustule has double membranes, the inner one at 

 some distance from the other on the dorsal side and with 

 an acute corner leaning against the transverse ends of the 

 connecting zone of the outer membrane. 



Foss.: Kk. Knjäsha, frequent in the marine strata. 



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



P. T. Cleve first remarked this arctic vicariating form 

 for Achnanthes brevipes, described it as a new species and 

 gave a figure of it in zonar view, showing the peculiar feature 

 of the double membranes. But, most probably, he has con- 

 fused it with another species, that I below have named 



