76 p. T. CLEVE, SYNOPSIS OF THE NAVICULOID DIATOMS. 



PitiH. subcapitata of G-regory has uninterrupted striae, but forms with a transverse fascia 

 are much more frequent. This species seems to graduate into Finn, interrupta, from which it 

 differs principally by its smaller size and less distinctly capitate ends. 



9. P. interrupta W. Sm. (1853). — V. linear, with parallel or slightly concave margins 

 and capitate ends. L. 0,0 5 to 0,o7 6; B. 0,oi3 mm. Axial area narrow, dilated in the middle to 

 a rhomboid space or transverse fascia. Striae 10 to 15 in 0,oi mm., strongly radiate in the middle, 

 convergent at the ends. 



Forma biceps: central area rhomboid. ~ P. biceps Greg. M. J. IV p. 8 PI. I f. 28 (1856). 

 P. interrupta fi "W. Sm. B. D. II p. 96. Nav. mesolepta /? producta Grun. Verh. 1860 p. 520 PI. IV 

 f. 22 a. Nav. bicapitata Lagst. Spitsb. D. p. 23 PL I f. 5. V. H. Syn. p. 78 PI. VI f. 14. Nav. 

 biceps A. S. Atl. XLV f. 69, 70. Nav. Termes A. S. Atl. XLV f. 67. Nav. mesolepta var. boryana 

 Pant. Ill PI. XXI f. 312. 



Fresh water: Spitsbergen! Norway! Sweden! Finland! Scotland (Greg.), Siberia! Japan! 

 Australia, Blue Mountains! Brazil! 



Forma stauroneiformis : central area a transverse fascia. Pinn. interrupta W. Sm. B. D. XIX 

 f. 184. Nav. int. A. S. Atl. XLV f. 72, 75, 76. Nav. Termes var. stauroneif. V. H. Syn. PL VI 

 f. 12, 13. A. S. Atl. XLV f. 71. 



Fresh water: Greenland! Norway (Romsdalen)! Sweden! Finland! England (W. Sm.), Ger- 

 many (Atl.), Bengal! Sandwich Islands! Surinam! Brazil! 



Var. crassior Grun. (1880). — V. gibbous in the middle and with broad, capitate ends 

 L. 0,035 to 0,042; B. 0,oo8 to 0,012 mm. Strise 13 to 14inO,oi mm. — Nav. globiceps var. crassior 

 Grun. A. D. p. 27 PL I f. 13. A. S. Atl. XLV f. 79 (without name). 



Brackish water: Jamal (Kara Sea)! Aland (Baltic)! 



Pinnul. biceps is closely connected with P. mesolepta, which differs only in the triundulate 

 margins. There is the same connection between them as between P. divergens and P. Legumen. 



10. P. mesolepta Ehb. (1843). — V. triundulated, with capitate ends. L. O.os to 0,o6; 

 B. 0,0 11 mm. Axial area narrow, dilated in the middle. Strise 10 to 14 in 0,oi mm. strongly 

 divergent in the middle and convergent at the ends. — Nav. mesolepta Ehb. Am. IV: 2 f. 4. KCtz 

 Bac. p. 101 PL XXVIII f. 73, XXX f. 34. V. H. Syn. p. 79 PL VI f. 10—11. Pinn. mesolepta 

 "W. Sm. B. D. XIX f. 182. Nav. mes. var. a, genuina Grun. Verh. 1860 p. 520. 



Fresh water: England! Scotland! Greenland! New Zealand! 



Var. stauroneiformis Grun. (1860). — Central area a transverse fascia, widened towards the 

 margins. — Grun. Verh. 1860 p. 520 PL IV f. 22 b. A. S. Atl. XLV f. 52, 53. 



Fresh water: Sweden (Rosslangen, Dpsala)! Finland! Greenland! Canada! Bridgewater, Maine! 



Var. angusta Cl. — V. narrow linear, triundulate. L. 0,065 to O.os; B. 0,oo9 to 0,oi mm. 

 Axial area wider. Strise 10 to 13 in 0,oi mm. — Nav. gracillima A. S. Atl. XLV f. 62. Cl. 

 M. D. N:o 103. 



Fresh water: Upsala, Sweden! Ringkiobing, Denmark (Atl.), Harz (Atl.), Maine, Bridge- 

 town! Demerara River! Rio Purus, Brazil! 



Var. polyonca Br^b. (1849). — V. triundulate; the median inflation being larger than the 

 others. L. 0,o6 to 0,o8; B. 0,012 mm. Area narrow, gradually expanded towards the middle to a 

 stauros. Strise 11 to 12 in O.oi mm., divergent in the middle, convergent at the ends. — Nav. 

 polyonca Br^b. in Kutz Sp. Alg. p. 85. V. H. Syn. p. 80 Suppl. A. f. 14. Nav. mesotyla A. S. 

 Atl. XLV f. 54, 55. 



Fresh water: Sweden (Loka, Atl., Upsala!) Belgium (V. H.). 



P. mesolepta is nearly connected with P. interrupta and analogous to P. nodosa, from which 

 latter it differs by its narrower area. The var. polyonca is in all respects to P. mesolepta what 

 the var. Formica is to P. nodosa. 



