KONGL. SV. VET. AKADKMIENG IIANDLINGAK. BAND 26. K:(i 2. 147 



14. S. UemerariB Cl. N. Sp. — V. linear, gibbous in the niiddle, witli bvoad cuneate end.s. 

 L. 0,045; B. 0,009 mm. Stanros liuear, pervious. (Terminal fissures, not seen). StritB very tine, 

 transverse in the middle, slightly radiate at tbe end.s. — Pl. Ill f. 15. 



Fresh water: Demerara River! 



Of tbis specie.s, remarkable for its form. I liave seen only a few specimens, in whicb I bave 

 not succeeded in niaking the terminal fissures visible, for whicb reason the description is somewhat 

 incomplete. 



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

 capitate ends. L. 0,o:i4 to 0,13; B. 0,oo6 to O.oi? mm. Stanros linear% reaching the margin or 

 not. Axial area indistinct. Strite 20 to 30 in ,0,01 mm. slightly radiate, finely pnnctate. — 

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



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

 into definite species. The numerous fresh-water species of Stauroneis, naraed by Ehrbnberg, are 

 fonnded on very slight difFerences in tlie outline, which is very variable, and they cannot be 

 identified, as no indication of the nnmber of strite 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 bad perhaps been to 

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

 very difPerent 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 nodule reaches usually 

 to the margin of the valve and corresponds to a transverse area, which however, is fre(}uently 

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

 be covered with shorter strife. 



A. Lanceolate forms, ivitli inorc or less protracted, not capitate ends. 



Var. siberica Grun. (1880). — V. lanceolate. L. 0, 064; B. 0,oi5 mm. Stauros not reaching 

 to tbe margin. Strite very fine (more than 30 in 0, 01 mm.). — Gkun. A. D. p. 48 Pl. III f. 65. 



Fresh water: Mouth of Jenisey (Grun.). 



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

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

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



Fresh water: Puy de Döme, fossil (Hérib.), Australia (Blne Mountains, Rieva Lagoons, 

 Austr. Alps)! 



Var. gracilis (Ehb. 1843?). — V. lanceolate. L. 0, 04 to 0,05; B. 0,oo8 mm. Stauros pervious. 

 Strite 27 in 0,oi mm. — S. c/rac. Ehb. Am. Pl. I: 2, f. 14 etc. 



Fresh water: Dovre, Norway! 



Var. hirosfris (Ehb. 1843?). — V. lanceolate. L. 0,o65 to 0,i3; B. 0,oi4 to 0,oi7 mm. 

 Strite 24 in 0, 01 mm. di.stinctly pnnctate. — S. hirostris Ehb. Am. Pl. II: 2 f. 1? S. anceps var. 

 Cl. D. f. Grönland and Argentina p. 12 Pl. XVI f. 5. St. gallica Hérib. a. Perag. D. d'Anvergne 

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



Fresh water: Puy de Döme, fossil (Hérib.), Waltham, Mass.! Argentina, Rioja! 



Var. derasa Grun. Ms. — V. narrow lanceolate, with somewhat protracted ends. L. O, o 5 to 

 0,07; B. 0,008 to 0,01 mm. Stauros broad pervious. Strite about 26 in (1, 01 mm. visible only 

 along the median line. 



Fresh water: Förarm 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. Strite 20 to 25 in 0,oi mm. — S. linearis Ehb. Am. 1: 2, f. 11 etc? iS'. anceps var. 

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



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



