12 ARKIV FÖR BOTANIK, BAND 14. N:0 9. 



Diploneis Boldtiana Cl. var. robusta n. var. Pl, 1, f. 8. 



Valve linear-elliptical with rounded ends, 28 — 40 |j. in 

 length, 14 — 16 u. in breadth. Furrows narrow, slightly bent 

 round the large, elliptical central nodule. Costae 8 — 9 in 

 10 a. Alveoli obsolete, rounded. 



Foss.: Ab. Hindersmossen. 



This form resembles D. Boldtiana Cl., but has a larger 

 central nodule and more distant costae. An intermediate 

 form with smaller nodule and 11 smooth costae in 10 [j. was 

 observed in samples from Sat., Panelia. 



Diploneis aestiva (Donk.) B. D. Tab. 1, f. 3. Cleve, 

 Syn. Nav. D. I, p. 94. 



Foss.: Kk. Knjäsha, rare [forma ,3). 

 Distr. {mar.): Arctic Sea, ubiquist. 



A few large specimens, fully agreeing with Donkin's 

 figure. 



Diploneis littoralis (Donk.) B. D. Tab. 1, f. 2. — V. H. 

 Syn. Suppl. B. f. 25. f. hybrida nob. 



As an intermediate form between this species and D. 

 aestiva I might consider a Diploneis, that is 40 u. in length, 

 20 "i. in breadth, and has narrow furrows, very slightly widened 

 round the central nodule, that is elongated. The costae are 

 9 in 10 [J. and alternate with apparently single rows of very 

 fine lineolae. 



Foss.: Kk. Knjäsha, rare. 



Distr. of the main form {mar.) : Arctic Sea, ubiquist. 



Diploneis Smithii (Bréb.) — Syn. Navicula elliptica W. 

 Sm. B. D. Tab. ]7, f. 152 a. The main form is stated by 

 Cleve to be 27—50 [j. in length (Syn. Nav. D. I, p. 96). 



A specimen, 60 <^ in length and thus graduating to the 

 following variety, was met with in Hindersmossen. 



Distr. {mar.): Greenl., East Arctic Sea, ubiquist. 



Diploneis Smithii (Bréb.) var. permagna n. var, — PI, 1, 

 f. 9, — Syn. Navicula Smithii Bréb. typ. A. S. Atl. Tab. 7, 

 f. 10 (according to Cleve = Diploneis major). 



