A. CLEVE-EULER, DIAT. FLORA OF FINLAND. 47 



groenlandica (and Achn. arctica). Also the diaphragms of 

 AcJui. groenlandica seem to be much less marked than in the 

 present species, not being visible at all on Cleve's figures 

 (D. Arct. Sea, Tab. 4, f. 23; Vega-Exp. D. Tab. 35, f. 3). In 

 ÖSTRUP's figure of »Achnanthes groenlandica Cl. var.», Kystd. 

 Gronl. Tab. 2, f. 17 they are represented. Finally, the dis- 

 tinctly quadrate puncta are coarser in Achn. septata, for 

 which reason they seem less distant, though there is almost 

 the same number of striae in 10 a in both species. 



From Achnanthes arctica this species is distinguished by 

 the presence of diaphragms, by the narrow fascia, by the 

 lack of an axial area and by the coarser alveoli. The size 

 is about the same. 



Kalyptoraphideae. 



Eschatoraphideae. 



Surirella Turp. 



Surirella biseriata Bréb. — V. H. Syn. Tab. 72, f. 1, 2. 



Ladoga. Foss.: Xyl. Kyrkslätt. 



Distr. {fresh iv.) : Ubiquist. 



Occurs together with the var. hijrons (Ehb.) Kütz. (re- 

 corded for Finland in Cleve's list) in until 325 a long, linear 

 specimens, attenuated towards the sharply acute ends. 1 V2 

 folds in 10 a. 



Surirella robusta Ehb. var. marginata n. var. — PI. 3, 

 f. 58. 



Costae marginal, leaving in the centrum of the valve a 

 blank, lanceolate space about a third as broad as the valve. 

 Length 200 <t, breadth 80 a. Costae 10 in 100 u.. 



Foss.: Ab. Hindersmossen; rare, among the type. 



Surirella tenera Greg. var. nervosa A. S. — Hust. Bac. 

 Wümme, Tab. 2, f. 4—5. 



Ladoga. Foss.: Ab. Hindersmossen; rather frequent. 



Distr. {fresh w.): Continent of Europe. 



Finlandian specimens are 130 — 150 a in length, 30 \}. in 

 breadth and have 4 folds in 25 a. 



