A. CLEVE-EULER, DI AT. FLORA OF FINLAND. 67 



Stoplianodiscus (Ehb.) Grux. 



Stephanodiscus Niagaras Grün. Franz Jos. L. D. Tab. 

 5, f. 1. — V. H. Syn. Tab. 95, f. 13. — Icon. nost. PL 3, 

 f. 72. 



Valve robust, not very convex, until 56 a in diameter. 

 Striae 10 in 10 a, composed of rather strong puncta in single 

 rows, that, however, at an other mise å point, can be resolved 

 into double rows of fine puncta, as in Stephanodiscns astraea. 

 Spins, inserted at some distance from the margin, alternate 

 with three rows of puncta. 



Foss. : Ab. Hindersmossen, rather common, associated 

 with Eunotia Clevei in strata from the Ancylus-e'poch. 



Distr. (fresh iv.): Larger lakes of North America and 

 Europe. 



Though I think the determination is correct, I give it 

 with reservation, having not had the opportunity of com- 

 paring the form from Finland with authentic specimens. If 

 so be the case, I quite agree wnth Mr östrup (Danske Diät. 

 j. Afl., p. 60) in the opinion, that Steph. Niagarae is hardly 

 specifically different from Steph. astraea. It is a stronger, 

 more luxuriant form, from which the recent Steph. astraea 

 may have developed in course of time. In reality, the 

 structure of the valves is certainly more similar than it ap- 

 pears to be in consequence of the thicker valves of Steph. 

 Niagarae. The presence of a little blank, central annulus is 

 a character, common to this large form and the larger Cyclo- 

 tellas, belonging to the section of Cyclotella comta. 



Biddulphia Gray. 



Biddulphia aurita (Lyngb.) Bréb. — V. H. Syn. Tab. 

 98, f. 4—9. Xord. Plankton, p. 105, f. 137. 



Foss.: Kk. Knjäsha. Koudajärvenpää, frequent. 

 Distr. {7nar.): Arctic Sea, ubiquist. 



Biddulphia obtusa (KCtz.) Ralfs. — V. H. Syn. Tab. 

 100, f. 11—14. 



Foss.: Kk. Knjäsha. 



Distr. (mar.): Ximrod Sound. 



