KONGL. SV. VET. AKADEMIENS HANDLINGAK. BAND. 27. N:0 3, 77 



11. P. globiceps GREfi. (1856). — V. strongly gibbous in the middle and with capitate 

 ends. L. 0,o3 to 0, 04; B. 0, 01 mm. Axial area indistinct; central area a broad, transverse fascia, 

 narrowed towards the margin. Strise 16 to 18 in 0,oi mm., divergent in the middle, convergent 

 at the ends. — M. J. IV Pl. I f. 34. Nav. glob. V. H. S. Syn. Suppl. A. f. 13. 



Brackish water: Scotland (Greg.), Anvers (V. H.), Strehlen (Grun.), Dörrenberg in Saxony! 

 Bengal! 



Var. Kroohii Grun. (1882). — L. 0, 01 5 to 0,u28; B. 0,oo5 to 0, 007 mm. Central area a wide 

 lanceolate space. Strise 15 to 17 in 0,oi mm. in the middle, 19 to 20 near the ends. — Nav. 

 Krockii Grun. Foss. D. Österr. Ung. p. 155 Pl. XXX f. 40. 



Brackish water: Hungary, (Soos Dept. Grun.), Gulf of Bothnia (Salmis to Torneå)! 



12. P. microstauron Ehb. (1843). — V. linear, with parallel margins and rostrate, broad 

 ends. L. 0,025 to 0,08; B. 0, 007 to 0, 009 mm. Axial area very narrow, frequently dilated in the 

 middle to a transverse fascia. Strite 12 in 0,oi mm., strongly divergent in the middle and con- 

 vergent at the ends. -- Stanroptera microstauron Ehb. Am. I: 4 f. 1; IV: 2 f. 2, Microg. XVI: 2 

 f. 4. Stauronein micr. Kutz. Bac. p. 106 Pl. XXIX f. 13. A. S. Atl. XLIV f. 16. Nav. divergens 

 f. minor A. S. Atl. XLIV f. 14, 34, 35, XLV f. 31 to 34. Nav. Bréhissonii v. subproclucta V. H. 

 Syn. p. 77 Pl. V f. 9. Pinn. interrupta Pedicino Ischia II f. 14. Nav. hicapitata var. hybrida 

 V. H. Syn. Pl. VI f. 9. Nav. Brébissonii Lägst. Spitsb. D. I f. 2 a. Pinn. Rabenhorstiana Hilse 

 Rab. A. Sachs. N:o 842 (1859). Nav. divergens var. prolongata Br. a. Héribaud D. d'Auvergne 

 p. 89 Pl. IV f. 1. 



Fresh water: Spitsbergen! Finmark! Sweden (Lappland, Areskutan, Skåne)! Finland (Lapp- 

 land to Åbo)! England! Germany! Kamtschatka! Australia (Blue Moiintains)! Greenland! North 

 America (Canada, Maine, White Monntains, Sierra Nevada)! 



P. microstauron is closely connected with P. Brébissonii and P. interrupta var. stauronei- 

 formis, which graduates into P. mesolepta. 



III. Divergentes. 



Artificial hey. 



J Termi 



^ . Terminal fissnres in contrary direction P. platycephala Ehb. 



— in the same direction 2. 



I Valve with undulated margins P. Legwmen Ehb. 



\ — not undulated 3. 



„ I Central area rounded P. karelica Cl. 



' \ — — a transverse fascia 4. 



Small forms 0,04 to 0,06 mm 5. 



Larger forms 0.07 to 0,36 mm 6. 



, j Striae very strongly divergent P. divergentissima Grun. 



I — somewhat divergent P. Brébissonii KiJTZ. 



,. , Striae 8 to 9 in 0,oi mm 7. 



b. 



I' 



11 to 12 in 0,01 mm P divergens "W. Sm. 



J Valve linear with parallel margins 8. 



' \ — — gibbons in the middle and at the ends P. Hartleyana Greg. 



Striae strongly radiate P episcopalis Cl. 



— slightly radiate P. Cardinaliculus Cl. 



{ 



13. P. diTergentissima Grun. (1880). — V. lanceolate with obtuse ends. L. 0,o3 to 0,035; 

 B. 0,00 7 mm. Axial area indistinct. Central area a broad fascia. Strise '13 in 0,oi mm. strongly 

 divergent in the middle and convergent at the ends. — Nav. nodulosa forma Lägst. Spitsb. D. 

 p. 22 Pl. II f. 2. Nav. divergentissima Grun. in V. H. Syn. Pl. VI f. 32. 



Fresh water: Spitsbergen (Ldt), North Iceland! Norway (Dovre)! Finland (Russian Lap- 

 land, Åbo)! Greenland! Canada! New Zealand! 



This little species is very characteristic and seems to belong to arotic and alpine regions. 



