44 



NITZSCHIA. 



I 



Fig. 126. Nitzschia 

 longissima (Nitzsckiella. 

 var. Closterium. 



Group 22. NlTZSCHIELLA RABENHORST. 



Valves with very eccentric keel and longly 

 rostrate apices. 



ANALYSIS OF SPECIES. 



f Valves terminating gradually in a rostrum ; transverse strire very visible N. Lorenziana. 



Valves terminating f Rostrum longer than the valve. Salt water 



-j abruptly in a species . . . N. longissima. 

 rostrum ; stria? -| 



scarcely or not | Rostrum shorter than the valve. Fresh water 



L visible. l_ species . . . . N. acicularis. 



N. longissima (Breb.) Ralfs. (in Pritch., p . 783; h.v.h. 



Atl., pi. 70, f. 1 and 2*), plate 17, fig. 568. 



Valves lanceolate, with rostrum excessively long and equal to or exceeding 

 the length of the valve. Keel very eccentric, with 6 to 12 dots in 1 c.d.m. 

 Stria?, about 16 in 1 c.d.m., excessively faint and difficult to be seen. Length, 

 attaining to 50 c.d.m. Breadth of valve, "4 to "8 c.d.m. 



Marine. Not yet found in Belgium, England (W. Sm., etc.), France (Breb.), Denmark, 

 (Heib). 



forma parva. (H.V.H. Atl., pi. 70, f. 3*), plate 17, fig. 569. 

 Small, and scarcely attaining a length of 12 to 13 c.d.m, 



