8 V. T. CL15VE, SYNOPSIS OF THK NAVICULOIl:) MaTOMS. 



A. Follis is intimately connected with A. serians and A. exilis and might, as the latter, be 

 considered as a variety of A. serians. Perhaps Nav. pyrenaica W. Sm. (Ann. Mag. Nat. Hist. XIX, 

 1857, p. 8 PI. II f. 5) is an intermediate form between A. Follis and A. serians, which cannot be 

 decided by the figure in Smith's paper. 



10. A.? exilis (Kdtz 1844), Grun. (1860). — V. narrow-lanceolate with protracted, capitate 

 ends. L. 0,o2i to 0,028; B. 0,oo5 mm. Axial and central areas indistinct. Striae about 30 in 

 0,01 mm. — Nav. exilis Kutz Bac. p. 95 PL IV f. 6 p. p. Geun. Verb. 1860 p. 553 PI. IV f. 30. 

 V. H. Syn. p. 101 PL XII f. 11, 12. Colletonema exile Grun. Verb. 1860 p. 571 PL VII f. 15? 

 Achnant. microcephalum W. Sm. B. D. LXI f. 380? 



Fresh, frequently slightly brackish water: Greenland! Norway, Dovre! Sweden, Lapland! 

 Russian Lapland! Gulf of Bothnia! Nordhausen (KtJTz). 



Var. thermalis Grun. (1880). — Lanceolate with less protracted, obtuse ends. L. 0,024; 

 B. 0,006 mm. Strife 27 in 0,oi mm. — N. serians var. thermalis Grun. V. H. Syn. PL XII f. 10. 



Habitat? 



Var. gomphonetnacea Grun. (1880). — V. lanceolate with rostrate ends, slightly asymmetrical 

 to the transverse axis. L. 0,022; B. 0,oo6 mm. Striae 30 in 0,oi mm. radiate in the middle, closer 

 towards the ends. — Gomphonema? vitreiim Grun. Casp. See Alg. p. 13. N. gomphonemacea Grun. 

 V. H. Syn. PL XII f. 13. 



Fresh water: Erlaf See near Mariazell (Grun.). 



By the var. thermalis A. exilis is closely connected with A. brachysira and A. serians. 



11. A.? bipunctata Grun. (1881). — V. linear, slightly biconstricted, with cuneate, broadly 

 truncate ends. L. 0,035; B. 0,oo6 mm. Median line with approximate central pores. Axial area 

 narrow. Central area a broad, transverse fascia. Striae about 30 in 0,oi mm. almost parallel, 

 very slightly radiate in the ends, punctate. — Nav. bip. V. H. Syn. PL XIII f. 7. 



Habitat? 



This species is unknown to me, and the diagnosis has been constructed from the figure 

 in V. H. Syn. 



Naviculse Heterosticlise Cl. 



Small, more or less elliptical, forms. Axial area narrow. Central area usually distinct. 

 Structure: fine striae, in the middle of the valve alternately longer and shorter, towards the ends 

 finer and radiate, finely, but usually distinctly, punctate; puncta forming undulate longitudinal rows. 



The species of this small group are closely connected with Naviculce punctatce, from which 

 they differ by the very fine punctation of the striae. Among the Naviculce lineolatce are several 

 similar forms, for instance N. bottnica, but they differ by the direction af the terminal striae. 



The few species of this section live in fresh water or in the mouths of rivers. 



Artificial key. 



.. I Valve biconstricted .... . . . . N. Tau Cl. 



■ \ — not — . . ... . . . g. 



„ j Ends rostrate . . . . . . 6, 



■ \ — not — . . . . . . 3. 



g f Central area indistinct . . . C. cocconeiformis Greg. 



■ \ — — orbicular . . 4 



j Median stria more coarsely punctate than the other jy^. limicola Cl. 



■ \ — — not — — — — . 5 



