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. diver gens and P. stauroptera. 



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

 subeapitate ends and slightly undulate margins. L. 0,o83 to 0,io5; B. 0,oi7 to0,oi8 mm. Median 

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

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

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

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



Fresh water: Sweden: Rosslangen (Calmar Ian)! PjesOrn Dept. (Skelleftea)! Ojasjo Dept. 

 (Blekinge)! Finl. Suomenniemi Dept. (Viborgs Ian)! Uurais socken (Vasa)! Pudasjarvi Dept. (Oster- 

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



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

 seems to come nearer to P. dirergens and P. legumen than to any other. 



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

 slightly capitate ends. L. 0,o7 to 0,i4; B. 0,oi5 to 0,o2 mm. Median line filiform, with curved 

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

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

 PI. XVIII f. 177. Nav. div. A. S. Atl. XLIV f. 9. Wollb 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 ("Waterford, Maine)! S. America (Demerara River, Santos)! 



Var. cuneata GtRUN. (1876). — V. with cuneate, subacute ends. L. 0,o7 5 to 0,i; B. 0,oi4 to 

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



Fresh water: Demerara River! 



Var. sublinearis 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.3 mm. Striae 12 in 0,oi mm. — A. S. Atl. XLIV f. 20, 

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



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

 Rio Purus, Brazil)! 



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

 to 0,15; B. 0,015 to 0,027 mm. Striae 8 to 11 in 0,oi mm. — Nav. div. var. ellipt. Gbun. Fr. Jos. 

 Land D. p. 98 PI. I £ 19. Nav. div. A. S. Atl. XLIV f. 6 — 7. Nav. cardinalis var. africana Beun 

 D. espfeces nov. p. 33 PI. XVI f. 9. Nav. viridis var. staurojphora Pant. Ill PI. VI f. 96 (1893)? 



Fresh water: Franz Jos. Land (Grun.), Norway (Tana Elf, Stavanger)! Sweden (Rosslangen 

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

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



Forma ornata Grun. — Central area with a semicirctilar row of dots on both sides of the 

 central nodule. L. 0,12; B. 0,oi7 mm. Striae 10 in 0,oi mm. — Bengal! 



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

 Median line oblique. Striae 11 in 0,o 1 mm. — Nav. Schweinfurtii 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 0,018 mm. Median line filiform, with approximate central pores and 

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

 valve in the middle widened to a transverse fascia. Striae 9 in 0,oi 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)! 



