108 p. T. CLEVE, SYNOPSIS OF THE NAVICULOID UIATOMSi 



Central pores of the median line approximate. Structure: small puncta arranged in parallel, trans- 

 verse and longitudinal rows, crossing each other at a right angle. Axial and central areas small 

 or indistinct. Connecting zone not complex. 



This group is closely related to the Section Fusifoi-mes, by the approximate central pores 

 and the structure of the valve, but the longitudinal striae of the valve are less distinct in Fusi- 

 formes. Some forms of Orthostichse seem to be connected with Gyrosigmaj The smaller forms of 

 this section, Nav. greyaria to N. microrhynchus, have no distinct longitudinal strise, but have been 

 placed here, as they seem to be connecteii with Nav. halophila. On the other hand they appear to 

 come near to JSfav. cryptocephala of the section Lineolataj. Some species have transversely dilated 

 central nodules, and have been considered as belonging to the genus Stauroneis, but there is very 

 little resemblance between there forms and the true Stauroneis (division of Microstigma,tic<e), in the 

 structure of the valve, which is the same as in other orthostichse. 



I Central nodul 



{ 



Artificial key. 



nodule dilated into a stauros . . . .... 11. 



not — — ■; 2. 



(Longitudinal stiiiae indistinct ....'. . ... . 3. 



\ — — distinct ... 6. 



J StrisB uninterrupted in tie middle 4. 



— interrupted . ... . . ... 5. 



Ends acute . .... . . N. microrhynchus Geun. 



— rostrate to capitate . . N. gregaria Donk. 



_ f Strise crossed by a longitudinal depression . . . N. Wankaremce Cl. 



\ — not — — — N. Kryokonites Cl. 



g I Terminal strise convergent N. holophila Grun. 



■ \ — — not — . .... .... 7. 



_ I "Valve broadly linear, with broad ends .... .... N. pbrtoniontana Cl. 



( — linear or lanceolate, narrowed towards the end . 8. 



{Transverse striae more distant than the longitudinal . . ■ N. cuspidata KtJTZ. 

 — — closer — — — N. Perrottetii Gbcn. 

 — — equidistant with — :./-., 9. 



g fEnds acute N. vitrea Cl. 



\ — rounded . . . ... 10. 



^Q j Striae 15 in 0,01 mm. . J\r. Ejellmanii Cl. 



1 — closer — . ... ... . . . N. O'Mearii Grtjn. 



f Stauros short . . . . . . . N. halearica Cl. 



11. '. — reaching half-way to the margin ... . . N. quarnerensis Grun. 



I — pervious — — — . ig. 



12 I ^^^''^ rhombic-lanceolate . . . N. Stodderi Greenl. 



\ — linear or linear-lanceolate ... .... 13. 



.. „ I Longitudinal striae more distant than the transyerso ... . . N. sulcata Cl. 



' \ — — closer — — — ... 14. 



Transverse stria 12 in 0,01 mm . . N. crucigera "W. Sm. 



— — about 26 in 0,oi mm - N. Spicula Hickib. 



u.{ 



1. N. gregaria Donk. (1861). — V. lanceolate, with rostrate-capitate ends. L. 0,oi5 to 

 0,035; B. 0,005 to 0,009 mm. Transverse strise 16 to 22 in 0,oi mm. Longitudinal stride indis- 

 tinct. — Donk. M. J. I p. 10 PI. I f. 10. B. D. p. 43 PI. VI f. 13. V. H. Syn. p. 85 PL YJIl 

 f. 12—15. Nav. cryptocephala W. Sm. B. D. PL XVII f. 155. Pedicino Ischia II f. 9—11. Nav. 

 lanceolata W. Sm. B. D. p. 46 PL XXXI f. 272? Nav. veneta Schum. P. D. II N. PL II f. 30. 

 Nav. Granum Avence Schum. P. D. N. II p. 56 PL II f. 36 (1867)? 



Brackish water: Sweden (Bohuslan)! England! Saxony (Salines Durrenberg)! Belgium' (V. H.) 

 France! South Africa! Argentina! 



