NITZSCHIA. 405 



var. Closterium. (N. C/os/erinm, W. Sm. ; H.V.H. All., pi. 70, 

 f. 5, 7 and S* ; Type No. 416), plate 17, fig. 570. 



Distinguished from the type-form by its rostra being curved on the same 

 side crosswise. Mean length, 26 to 32 c.d.m. 



Brackish water. Blankenberghe. England (W. Sm., Comber, Norman, Stolt. ). Ireland 

 (O'Meara). France. 



var. reversa. (N. reversa., IV. Sm. /) 



Differs from the preceding by its rostra curved in opposite directions, 

 10 to 14 carinal dots in 1 c.d.m. Length, 7 to 20 c.d.m. 



Marine. England (Lewes, W. Sm. ! Norman, Stolt.). France (Br6b.). Holland (T. 

 Spree). Denmark (Heiberg). 



In the gatherings from the herbarium of Professor W. Smith we have 

 found perfect valves, which has enabled us clearly to prove that Wm. Smith's 

 form is a Nitzschia and not a Synedra, as Mr. Grunow thought (Arct. Diat, p. 

 100). The carinal dots are only visible with difficulty. It requires an 

 excellent immersion objective to distinguish them clearly. There are 10 of 

 them at the apices of the valve, and 14 to 16 in the median portion. It was 

 probably the carinal dots that Prof Smith described as indistinct marginal 

 striae. 



N. acicularis, W. Sm. (S.B.D., i., p. 43, pi. 15, f. 122 ; H.V.H. 



Atl, pi. 70, f. 6*; Type No. 415), plate 17, fig. 571. 



Valve lanceolate, with rostrum shorter than the valve. Carinal dots 

 18 in 1 c.d.m. Strice not visible, or at least only traces visible at the margins 

 of the valve. Length, 6 to 7 c.d.m. 



Fresh water. Brussels (Delogne), Antwerp, etc. England (W. Sm., Norman, etc.) 



N. Lorenziana Grun. ! (Arct. Diat., p. 101 ; H.V.H. Atl., pi. 70, f. 

 12*), plate 17, fig. 572. 



Valve very narrowly lanceolate, very slightly attenuated into curved rostra, 

 with apices turned in opposite directions. Carinal dots 6 or 7 in 1 c.d.m., 

 conspicuous up to the apex of the rostra ; striae 13*5 to 14 in 1 c.d.m. at the 

 middle of the valve, and conspicuous, becoming less visible and more compact 

 (20 in 1 c.d.m.) towards the apices of the valve. Length, 13 to 19 c.d.m. 

 Breadth of valves, '6 to 7 c.d.m. 



Brackish water. Not yet found in Belgium. 



