392 NITZSCHIA. 



Group 12. Bacillaria. 



Keel central or almost central, with dots not elongated. Frustules 

 straight. Striation conspicuous. 



ANALYSIS OF SPECIES. 

 Keel almost central, frustules united in a stratum. . . N. paradoxa 



N. paradoxa (Gmel.) Grun. ! {Bacillaria paradoxa Gmel.\ 

 H.V.H. Atl., pi. 61, f. 6* ; Type No. 388), plate 15, fig. 518. 



Valves narrowly lanceolate, with apices feebly rostrate. Keel almost 

 central, with 6 to 8 coarse round dots in 1 c.d.m. Strice 20*5 to 22^5 in 

 1 c.d.m. Frustules united in a stratum, displaced by a sliding movement of 

 one frustule over another. Length, about 6 c.d.m. 



Brackish water. Blankenberghe, Ostend, Antwerp. England, Ireland, and almost everywhere. 

 Sometimes found in water containing only a trace of salt. Canal at Louvain (P. Gaut. ). 



var. major. (H.V.H. Atl., pi. 61, f. 7*), plate 16, fig. 519. 



Group 13. VivaClS. 



Valves semi-lanceolate, with margins showing elongated carinal 

 dots. Valves similar to those of Hantzschia, but not showing (like 

 those of the species of that genus) a vestige of a central nodule. 



ANALYSIS OF SPECIES. 



f Valve semi-lanceolate, strongly arcuate, very small, with rostrate apices ; 



striae very delicate . . N. Petitiana. 



I Valve semi-lanceolate elliptic, large, with rostrate apices ; stria; rather 



[ robust . . . . . N. vivax. 



N. vivax W. Sm. ! (S.B.D., i., p. 4 t, pi. 31, f. 267; H.V.H. 

 Atl., pi. 62, f. 1-2* ; in Type No. 389), plate 33, fig. 877. 



Valve semi-lanceolate, elliptic, with ventral margin straight, dorsal margin 

 arcuate, apices produced rostrate. Carinal dots somewhat elongated, 6 in 1 

 c.d.m. ; striae 12 in i c.d.m., finely punctate. Frustules linear. Length, 10 

 to 16 c.d.m. Breadth of valves, 1*3 c.d.m. 



Marine. England (W. Sm., Comber, Norman), Ireland (O'Meara). 



