396 NITZSCH1A. 



N. Brebissonii W. Sm. ! (S.B.D., i., p. 38, pi. 31, f. 226 ; H.v.H. 



Atl., pi. 64, f. 4 and 5* ; Type No. 393), plate 16, fig. 530. 



Valves straight, or curved, or arcuate, or sigmoid ; about 5 carinal dots in 

 1 c.d.m., apices rather abruptly attenuate, acute; striae very robust, 9 to 1 1 in 

 1 c.d.m. Length, 22 to 24 c.d.m. Breadth of valve, 1*3 to 1*5 c.d.m. 



Brackish water. Heyst (Deby). Antwerp. England (W. Sm., Comber, Norman), Ireland 

 (O'Meara). France, etc. 



Group 17. SlGMATA. 



Valves still less sigmoid, keel somewhat more eccentric than in the 

 preceding group. Girdle face sigmoid, with apices produced. 



! 



ANALYSIS OF SPECIES. 



Keel with coarse, very projecting dots . . . N. fasciculata. 



Keel with rather delicate dots . . . . N. Sigma. 



N. Sigma, W. Sm. ! (S.B.D., i, p. 39, pi. 108; H.v.H. Atl, pi. 



65, f. 7 and 8* ; Type No. 394), plate 16, fig. 531. 



Valves linear, somewhat sigmoid, with apices very slightly produced. Keel 

 eccentric, with 7 to 9 dots in 1 c.d.m. Striae fine, 22 to 24 in 1 c.d.m. Girdle 

 face sigmoid, with tapering apices. Length, attaining 25 c.d.m. Breadth, a 

 little more than ro c.d.m. 



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

 Ireland (O'Meara). France, Bahnsie. Finmark. 



var. intercedens Grun. (H.V.H. Atl, pi. 66, f. 1*), plate 16, fig. 

 532. 



Large and generally very much curved, with 6 to 7 carinal dots, and 

 27 or 28 striae in 1 c.d.m, the valve being about 1 c.d.m. broad, and up 

 to 30 c.d.m. long. 



Brackish water. Antwerp (Scheldt, Belleroche). 



var. rigida (Kiitz.) Grun. (Amp/iipleura rigida K'utz. ; A. 

 sigmoidea, W. Sm. ; H.V.H. Atl, pi. 66, f. 2* ; in Type No. 395), plate 

 16, fig. 533- 



Valve narrowly lanceolate, sigmoid, with 7 to 9 carinal dots, and 30 or 

 31 striae in 1 c.d.m. Valves attaining a length of 20 c.d.m, and a 

 breadth of 8/x 



Freshwater. Brussels, Antwerp. England (W. Sm., Comber, Norman). Scotland. 

 Ireland (O'Meara). 



var. rigidula Grun. (H.V.H. Atl, pi. 66, f. 8*; Type No. 396), 

 plate 16, fig. 534. 



