NITZSCHIA. 389 



N. dubia W. Sm. ! (S.B.D.,i., p. 41, pi. 13, f. 112 ; H.v.H. Atl., 



pi. 59, f. 9-12*; Type No. 3S2), plate 15, fig. 508. 



Valves linear, somewhat constricted at the median portion, with sub- 

 rostrate apices; stria? fine, 21 to 24 in 1 c.d.m. ; keel with 9 or 10 dots in 

 1 c.d.m., slightly prolonged on the valve. Length, about 9 to 16 c.d.m. 



Fresh water. Antwerp. Schaerbeeck (Delogne). England (W. Sm. !). 



N. thermalis(Kutz.)Grun. ! (Arct. Diat., p. 78; H.v.H. Atl., 



pi. 59, f. 20 ; in Type No. 74 var. litloralis), plate 15, fig. 509. 



Differs from the preceding species by its narrower valves and round carinal 

 dots, the two median of which are somewhat distant. Striae fine, about 28 

 in 1 c.d.m. ; carinal dots about 7 or 8 in 1 c.d.m. Length, about 8 to 

 10 c.d.m ; breadth, about 1 c.d.m. 



Fresh water. Aid. Lieg. (De Wild.). Ireland (O'Meara). 



var. intermedia Grun. (H.V.H. Atl., pi. 59, f. 15-19*), plate 15, 

 fig. 510. 



Valves small (5 to 6 c.d.m.) and narrow (somewhat more than "5 

 c.d.m., with small carinal dots (9 in 1 c.d.m.), the two median of 

 which are slightly distant ; stria? very fine, about 32 in 1 c.d.m. 



Freshwater. Ard. Lieg (DeWild.). 



var. littoralis Grun. (H.V.H. Atl., pi. 59. f. 21). England. 



N. commutata Grun. (Arct. Diat., p. 79; H.V.H. Atl., pi. 59, 

 f. 13 and 14*), plate 15, fig. 511. 



Valve longly linear, constricted at the median portion, with apices 



distinctly rostrate, rostrum obtuse. Carinal dots round, the two median 



distant. Stria? fine, 21 to 24 in x c.d.m. Carinal dots 9 or 10 in 1 c.d.m. 

 Length, 5 to 7 c.d.m. Breadth, 1-25 to 175 c.d.m. 



Brackish water. Not yet found in Belgium. England (W. Sm.) 



Group 7. BlLOBATVE. 



Differs from the preceding group by the more central position 

 of the keel. 



N. bilobata W. Sm. (S.B.D., i., p. 42, pi. 15, f. n 3; h.v.h. 

 Atl., pi. 60, f. t*), plate 15, fig. 512. 



Valve linear, lanceolate, constricted at the median portion, with apices 

 abruptly attenuate, rostrate, acute. Keel almost central, with carinal dots 



