KONGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 26. N:0 2. 147 



14. S. DemerarsB Cl. N. Sp. — V. linear, gibbous in the middle, with broad cuneate ends. 

 L. 0,04 5; B. 0,009 mm. Stauros linear, pervious. (Terminal fissures, not seen). Striae very fine, 

 transverse in the middle, slightly radiate at the ends. — PI. Ill f. 15. 



Fresh water: Demerara River! 



Of this species, remarkable for its form, I have seen only a few specimens, in which I have 

 not succeeded in making the terminal fissures visible, for which reason the description is somewhat 

 incomplete. 



15. S. anceps Ehr. (1843). — V. lanceolate to linear-lanceolate, with rostrate or rostrate- 

 capitate ends. L. 0,024 to 0,13; B. 0,oo6 to 0,oi7 mm. Stauros linear, reaching the margin or 

 not. Axial area indistinct. Striae 20 to 30 in 0,oi mm. slightly radiate, finely punctate. — 

 S. anceps Ehb. Am. PL II: 1, f. 18. 



S. anceps is extremely variable, and it does not appear to me possible to separate the forms 

 into definite species. The numerous fresh-water species of Stauroneis, named by Ehrenbebg, are 

 founded on very slight differences in the outline, which is very variable, and they cannot be 

 identified, as no indication of the number of strise exists. Moreover the forms included here under 

 the name of S. anceps, pass gradually, without any limit, into others, which can scarcely be di- 

 stinguished from smaller forms of S. Phoenicenteron. The simplest method had perhaps been to 

 unite S. anceps and S. Phoenicenteron, but the species would then have comprised, as extremes, 

 very different forms. From a practical point of view it seems to be best to arrange the forms 

 into a few varieties, however arbitrary the limits may be. The central nodiile reaches usually 

 to the margin of the valve and corresponds to a transverse area, which however, is frequently 

 narrower than the central nodules. Under good lenses the marginal part of the stauros seems to 

 be covered with shorter strife. 



A. Lanceolate forms, ivith more or less protracted, not capitate ends. 



Var. siberica Grun. (1880). — V. lanceolate. L. 0,064; B. 0,015 mm. Stauros not reaching 

 to the margin. Strise very fine (more than 30 in 0,oi mm.). — Grun. A. D. p. 48 PL III f 65. 



Fresh water: Mouth of Jenisey (Grun.). 



Var. hyalina Br. a. Pbrag. (1893). — V. lanceolate, with very protracted ends. L. 0,04 to 

 0,085; B. 0,009 to 0,012 mm. Stauros pervious. Strise very fine. — Br. a. Perag. in Herib. D. 

 d'Auvergne p. 78 PL III f. 19. 



Fresh water: Puy de Dome, fossil (Herib.), Australia (Blue Mountains, Rieva Lagoons, 

 Austr. Alps)! 



Var. gracilis (Ehb. 1843?). — V. lanceolate. L. 0,04 to 0,o5 ; B. 0,oo8 mm. Stauros pervious. 

 Striae 27 in 0,oi mm. — S. grac. Ehb. Am. PL I: 2, f. 14 etc. 



Fresh water: Dovre, Norway! 



Var. hirostris (Ehb. 1843?). — V. lanceolate. L. 0,065 to 0,13; B. 0,oi4 to 0,017 mm. 

 Striee 24 in 0,oi mm. distinctly punctate. — S. hirostris Ehb. Am. PL II: 2 f. 1? S. anceps var. 

 Cl. D. f. Gronland and Argentina p. 12 PL XVI f. 5. St. gallica H:^rib. a. Perag. D. d'Auvergne 

 p. 77 PL III f. 21 (1893). 



Fresh water: Puy de Dome, fossil (Herib.), Waltham, Mass.! Argentina, Rioja! 



Var. derasa Grun. Ms. — V. narrow lanceolate, with somewhat protracted ends. L. 0,05 to 

 0,07; B. 0,008 to 0,01 mm. Stauros broad pervious. Strise about 26 in 0,oi mm. visible only 

 along the median line. 



Fresh water: Forarm in Asnen, Sweden, fossil! 



Var. linearis Ehb. (1843). — V. with parallel margins, rostrate. L. 0,045 to 0,05; B. 0,oo8 

 to 0,012 mm. Striai 20 to 25 in 0,oi mm. — S. linearis Ehb. Am. 1: 2, f. 11 etc.? S. anceps var. 

 lin. V. H. Syn. p. 69 PL IV f. 7, 8. 



Fresh water: Holstein! Belgium (V. H.), Australia, Blue Mountains! 



