158 



STAURONEIS. 



U-'Ji 



GENUS 6. STAURONEIS EHR, 1843. 



Frustules free or united in a small number, 

 differing from Navicula by the central nodule 

 being transversely dilated into a stauros. 

 Endochrome similar to that of the Navicula. 



We include in the genus Stauroneis the following 

 groups which have been raised to genus rank by 

 various authors : 



Fig. 30. Stauroneis 

 Phcenicenteron Ehr. 



Frustules not con 

 tained in mucous 

 tubes 



f Frust 

 ' j solitary. 



' Valv 



( Valves with decussating striae. Staurogramma Rat). 1853. 



Staurosigma Grun. 1860. 

 Pleurostauron Ra??. 1859. 

 Endostauron Grun. 1868. 



( Valves with sigmoid raphe 

 uiDes . . I 



^ Valves cohering in filaments. 



I. Frustules contained in mucous tubes (Schizonema W. Sm. ) 



ANALYSIS OF SPECIES. 



'5 





Valves 



with 

 margins 

 not un- 

 dulate. 



Valves 

 not per- 

 ceptibly 

 attenuate 

 rostrate. 



bifurcate 



Stauros 



very 

 broad. 



f Valve not ter- /Valve broad 



minated by a) and large . S. Phcenicenteron. 



L l f n _L raphe j Valve small 



^ and narrow S. gracilis. 



f Lumen very large, 



J raphe bifurcate. 

 Frustules united 

 together many at 

 a time . . S. acuta 



Valve 

 ter- 

 minated 

 by a 



lumen. 



I 



Lumen small, 

 j raphe si mple. 

 ^ Frustules isolated S. Gregorii. 



Stauros 

 narrow. 



( Valve very long, very narrowly 

 i lanceolate . . . S. spicula. 



^ Valve short, broadly lanceolate S. salina. 



^ Valves with apices attenuate-rostrate . . . S. anceps. 



Valves short and broad ; terminal lumen very large . S. Smithii. 

 Valves long and narrow ; terminal lumen very small . S. Legumen. 



, Raphe oblique, sub-sigmoid . . . . . . S. obliqua. 



Valves 



with 

 margins - 

 triundu 



late. L 



