206 NAVICULA. 



My group, Aspera, corresponds with the genus Trachyncis of Prof. Cleve, 

 a genus which appears to me to be well founded, but I have not provisionally 

 admitted it here, in order not to interfere too much with the order adopted in 

 the Synopsis. 



VIII. Stauroneideae. 



f Apices capitate ; puncta interrupted 

 Hyaline space here and there . . N. Tuscula. 



narrow, -\ 



appearance j striae radiate. | Apices not capitate ; stauroneiform 

 caused by a | ^ space showing an isolated bead . N. mutica. 



Stauroneiform 

 appearance 

 caused by a 



hyaline space 



| Hyaline space excessively broad ; valve linear-elliptic ; 



t striae perpendicular to the raphe . . \*N. Pinnularia. 



Stauroneiform c Valve lanceolate, neither rostrate nor undulate . N. crucicula. 



appearance, 

 caused by more -J Valve tri-undulate, with apices apiculate-rostrate . N. integra. 



distant median 

 I. striae. i. Valve linear-subelliptic . . . . N. subinflata. 



A . Stauroneiform appearance caused by a hyaline space. 



a. Hyaline space narrow, valve with radiate striae. 

 * PUNCTA FORMING IRREGULAR LONGITUDINAL LINES. 



N. TllSCllla Ehr. (Stauroneis punctata Ruiz., Bac, p. 106, pi. 21, 

 f. 9. ; H.V.H. Atl., pi. 10, f. 14; Type No. in), plate 4, fig. 166. 



Valves elliptic, with apices strongly rostrate capitate. Raphe surrounded 

 by a narrow hyaline zone, dilated round the central nodule into a pseudo- 

 stauros irregularly subdivided. Striae 7 or 8 in 1 c.d.m., becoming radiate 

 from the middle of the valve, finely divided transversely and with frequent 

 interruptions, the entirety forming irregular longitudinal lines. Length, about 

 8 c.d.m. Breadth, 2*5 c.d.m. 



Fresh and brackish water. Antwerp (H.V.H.) Orval (Del.) England (Wm, Sm. and W. 

 Arnott), and probably elsewhere. 



** PUNCTA NOT FORMING LONGITUDINAL LINES. 



N. mutica Kutz. ! (Stauroneis Cohnii Hilse \ H.V.H. Atl., pi. 10, 

 f. 17*; Type No. 113), plate 4, fig. 167. 



Valve elliptic or elliptic-lanceolate. Raphe surrounded by a narrow 

 hyaline zone, which, round the central nodule, is dilated into a pseudo- 

 stauros, on one of the sides of which a coarse isolated bead is seen. Striae 

 radiate with well marked puncta, 15 to 18 in 1 c.d.m. Length, 1 to 2 c.d.m. 

 Breadth, about 7 c.d.m. 



Brackish water. Piles in the Scheldt at Antwerp. Ostend, etc. England (Kitton, Norman). 

 Ireland (O'M.) and probably throughout Europe. 



