KONGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 27. N:0 3, 79 



the margin being often very slight, in which case it is impossible to distinguish it from certain 

 forms of P. divergens and P. stauroptera. 



17. P. platycepliala Ehb. (1854). — V. linear, 5 to 6 times longer than broad, with broad, 

 subcapitate ends and slightly undulate margins. Ij. 0,o8.3 to 0,io5; B. 0,oi7 to0,oi8mm. Median 

 line filiform with terminal fissures in contrary directions. Axial area distinct, about V., of ^^^ 

 breadth of the valve. Central area a more or less perfect fascia. Striee divergent in the middle, 

 convergent at the ends, 12 in 0,oi mm. — Stauroptera platycepliala Ehb. M. Gr. XVII: ii f. 9. 

 Pinnul. platyc. Cl. Diat. of Finl. p. 20 Pl. II f. 1. 



Tresh water: Sweden: Rosslängen (Calmar län)! Pjesörn Dept. (Skellefteå)! Öjasjö Dept. 

 (Blekinge)! Finl. Suomenniemi Dept. (Viborgs län)! Uurais socken (Vasa)! Pudasjärvi Dept. (Öster- 

 botten)! Scotland (Grove), France: Lac Gerardmer (Vosges)! 



P. platycephala is an isolated species, which shews no close relation to any known form. It 

 seems to come nearer to P. divergens and P. legtmten than to any other. 



18. P. divergens "W. Sm. (1853). — V. lanceolate, gradually attenuated to the obtnse or 

 slightly capitate ends. L. 0,07 to 0,i4; B. O.ois to 0, 02 mm. Median line filiform, with curved 

 terminal fissures. Axial area narrow, distinct, widened in the middle to a transverse fascia. Strise 

 11 to 12 in 0,01 mm., strongly divergent in the middle, convergent at the ends. — Br. D. p. 57 

 Pl. XVIII f. 177. Nav. div. A. S. Atl. XLIV f. 9. Wolle D. of N. A. XIX f. 21. 



Fresh water: Sweden (Lappland to Blekinge)! Norway (Stavanger)! Scotland (Premney 

 Peat, W. Sm., Dolgelly earth W. Sm., Loch Kinnord!) Finland! Bengal! New Zealand! Sandwich 

 Islands! N. America ("W återförd, Maine)! S. America (Deraerara River, Santos)! 



Var. cuneata Grun. (1876). — V. with ciineate, snbacute ends. L. 0,o7 5 to 0,i ; B. 0,oi4 to 

 0,02 mm. Central area a narrow fascia. Strise 11 in 0, 01 mm. — A. S. Atl. XLIV f. 10, 11. 



Fresh water: Demerara River! 



Var. suhlinearis Cl. — V. elleptic-linear, gradually tapering from the middle to the obtuse 

 ends. L. 0,o8 to 0,io; B. 0,oi4 to 0,oi.'5 mm. Stria 12 in 0,oi mm. — A. S. Atl. XLIV f. 20, 

 23. Nav. procera Pant. II p. 52 Pl. I f. 8 (1889)? 



Fresh water: New Zealand! America (Bemis Lake, White Mountains, Waterford, Maine; 

 Rio Purus, Brazil)! 



Var. elliptica Grun. (1884). — V. broad, linear to elliptical, with roiuided ends. L. 0,o7 5 

 to 0,15; B. 0,015 to 0,027 mm. Strite 8 to 11 in 0, 01 mm. — Nav. div. var. ellipt. Grun. Fr. Jos. 

 Land D. p. 98 Pl. I f 19. Nav. div. A. S. Atl. XLIV f. (? — 7. Nav. cardinalis var. africana Brun 

 D. espéces nov. p. 33 Pl. XVI f. 9. Nav. viridis var. staurophora Pant. III Pl. VI f. 96 (1893)? 



Fresh water: Franz Jos. Land (Grun.), Norway (Tan a Elf, Stavanger)! Sweden (Rosslängen 

 in Kalmar län, Öjasjö in Blekinge)! Finland! Scotland (Island of Lewis)! Australia (Blue Moun- 

 tains)! Greenland! Monmouth (Atl.), Demerara River! S. W. Africa, ömbika (Brun Coll.)! 



Forma ornata Grun. — Central area with a semicircular row of döts on both sides of the 

 central nodule. L. 0,12; B. 0,017 mm. Striee 10 in 0, 01 mm. — Bengal! 



Var. Schtveinfurtii A. S. (1876). — L. 0, 11 to 0,12; B. 0,02 mm. Axial area more narrow. 

 Median line oblique. Striee 11 in 0,oi mm. — Nav. Schtveinfurtii A. S. Atl. XLIV f 4, 5. 



Fresh water: Scriba Gattas (Atl.). 



19. P. Cardinaliculus Cl. N. Sp. — V. linear, with parallel margins and rounded ends. 

 L. 0,08 to 0,1; B. 0,015 to 0,0 18 mm. Median line filiform, with approximate central pores and 

 short, bayonet-shaped terminal fissures. Axial area less than V3 ^^ broad as the breadth of the 

 valve in the middle widened to a transverse fascia. Striae 9 in 0, 01 mm., almost parallel or 

 slightly divergent in the middle and convergent at the ends. — Pl. I f. 12. 



Fresh water: Scotland (Grove Coll.)! America (Canada, Crane Pond, French Pond, Houghton 

 Mich., Mexico)! 



