NITZSCHIA. 397 



Differs from the preceding variety by its smaller size and breadth, 8 

 to 10 carinal dots, and 30 or 31 striae in 1 c.d.m. Length, about 6 to 7 

 c.d.m. Breadth, less than 0*5 c.d.m, 



Fresh water. Rouge-Cloitre (Delogne). 



var. Sigmatella Grun. (H.V.H. Atl., pi. 66, f. 6 and 7* ; Type No. 

 397), plate 16, fig. 535. 



Valves very narrowly lanceolate, sigmoid, with S to 1 1 carinal dots in 

 1 c.d.m., and 25 or 26 striae in 1 c.d.m. Valves attaining 32 c.d.m., 

 (sometimes, but rarely, even 45 c.d.m.), and about 5 c.d.m. in breadth. 



Brackish water. Ostend. 



N. fasciculata Grun. (Honuzorfadia sigmoidea, IV. Sm. ; 

 H.V.H. Atl., pi. 66, f. n-13*), plate 16, fig. 536. 



Valve more or less sigmoid, sometimes almost straight. Keel with coarse 

 dots, somewhat elongated, 5 or 6 in 1 c.d.m. Striae fine, 28 or 29 in 1 c.d.m. 

 Frustules often united in small fascicles. Length, 5 to 10 c.d.m. 



Marine or brackish. Ostend (Grunow), Antwerp. England (W. Sm.). 



Group 18. ObtuSjE. 



Analogous to the preceding groups, from which it is distinguished 

 by the keel, which in the middle of its length shows an inflection at 

 the internal portion, and at the same part two somewhat distant dots 

 between which the rudiment of a nodule appears. 



ANALYSIS OF SPECIES. 



Keel showing in the middle of its length an inflexion, at which the two median 

 dots are somewhat distant, and between them the rudiment of a nodule 

 is shewn . . . . . . . N. obtusa 



N. obtusa W. Sm. ! (s.b.d., i, p. 39 , pi 13, f. 109; h.v.h. 



Atl., pi. 67, f. 1* ; Type No. 398), plate 16, fig. 537. 



Valve linear, with apices rounded or abruptly attenuate unilaterally. 

 Keel with 5 or 6 coarse dots. Median inflexion very visible. Striae fine, 26 

 or 27 in 1 c.d.m. Length, 12 to 25 c.d.m. Breadth of valves somewhat less 

 than - 8 to "9 c.d.m. 



Brackish water Blankenberghe (H.V.H.), Aid. Liege (De Wild.), England (W. Sm. ! Stolt.), 

 Denmark, Holland, &c. 



var. scalpelliformis. (Arct. Diat., p. 92 ; H.V.H. Atl., pi. 67, f. 2*), 

 plate 16, fig. 538. 



