8 r. T. CLKVE, SYNOPSIS OK THE XAVICl LOID DIATOMS, 



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

 considered as a variety of A. serians. Perliaps 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 (Kutz 1844), Grun. (1860). — V. narrow-lanceolate with protracted, capitate 

 ends. L. 0,o2i to 0,o28; B. 0,oo5 mm. Axial and central areas indistinct. Striae about 30 in 

 0,0 1 mm. — Nav. exilis Kutz Bac. p. 95 PI. IV f. 6 p. p. Grun. Verh. 1800 p. 553 PI. IV f. 30. 

 V. H. Syn. p. 101 PI. XII f. 11. 12. Colletonema exile Grun. Verh. 1860 p. 571 PI. VII f. 15? 

 Achnant. mierocephalum W. Sm. B. I). LXI f. 380? 



Fresh, freqiiently 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,o24; 

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



Habitat? 



Var. gomphonemacea 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. — Gowphonema? ritrcnm Grun. Casp. See Alg. p. 13. N. gomphonemacea Grun. 

 V. H. Syn. PI. XII f. 13. 



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



By the var. thcnnalis A. exilis is closely connected with A. hrachysira and A. serians. 



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

 truncate ends. L. 0,0.35; B. 0,oof) 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. PI. XIII f. 7. 



Habitat? 



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

 in V. H. Syn. 



Naviculse Heterostichse 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 us^^ally distinctly, punctate; puncta forming undulate longitudinal rows. 



The species of this small group are closely connected with Nariculfc 2>><>tefaf(X, from which 

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

 similar forms, for instance N. holfnica, 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. 



biconstricted N. Tau Cl. 



2. 



Ends rostrate 6. 



Artificial key 



^ j Valve biconstri 

 \ — not — 



2 i 



• \ — not — 3. 



( Central area indistinct C. cocconelformis Greg. 



' \ — — orbicular 4. 



. j Median striiB more coarsely punctate than the other N. limicola Cl. 



■ I — — not — — ■ — — 5. 



