8 1'. T. CLEVE, SYNOPSIS OF THE XAVICULOIt) DlATOMS. 



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

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

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

 decided by tbe figure in Smith's paper. 



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

 ends. L. 0,02i to 0,028; B. 0, 005 mm. Axial and central areas indistinct. Strise about 30 in 

 0,01 mm. — Nav. exilis KtJTZ Bac. p. 95 Pl. IV f. 6 p. p. Grun. Verb. 1860 p. 553 Pl. 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. microcephaluni W. Sm. B. D. LXI f. 380? 



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

 Russian Lapland! Gulf of Botbnia! Nordhausen (Kutz). 



Var. therinalis G-run. (1880). — Lanceolate with less protraeted, obtuse ends. L. 0,024; 

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



Habitat? 



Var. gomphonemacea Grdn. (1880). — V. lanceolate with rostrate ends, slightly asymmetrical 

 to the transverse axis. L. 0,022; B. 0,oo6 mm. Stria3 30 in 0, 01 mm. radiate in the middle, closer 

 towards the ends. — Gonqjhonema? vitreum 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, 01 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 strise, 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 gronp are closely connected with Naviculw punctatce, from which 

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

 similar forms, for instance N. hottnica, but they difter by the direction af the terminal strise. 



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



Artificial hey. 



^ I Valve biconstricted N. Tau Cl. 



not — 2. 



i 



. j Median striiE more coarsely punctate tlian tlie otlicr N. limicola Cr,. 



1 — — not — - — — 5. 



Ends rostrate 6. 



not — 3. 



entral area indistinct C. cocconeiformis Greg. 



— orbicular 4. 



