NITZSCHIA. 385 



var. elongata Grun. (H.V.H. At!., pi. 57, f. 3*), plate 15, fig. 492. 



Valves linear, with cuneate apices ; striae 5 or 6 in 1 c.d.m. Length of 

 valves, 6 to 1 1 c.d.m. Breadth, 2 to 2-5 c.d.m. 



Marine. Mixed with the type-form. Ostend (Deby.). 



N. Tryblionella HantzSCh (Trybliondla Hantzschiana Grun. . 

 H.V.H. Atl., pi. 57, f. 9, 10 and 15* ; Type No. 375), plate 15, fig. 493. 



Valve elliptic-lanceolate, with subacute apices, showing a broad con- 

 spicuous sulcus; striae robust, 5 to 7 in 1 c.d.m., between which appear stria?, 

 fine, delicately punctate. Length, 8 to 1 1 c.d.m. Breadth, 2 to 3 c.d.m. 



Fresh and brackish water Not yet found in Belgium. England (Stolt.). Ireland (O'Meara). 



var. Levidensis. (T. Levidensis W. Sm. ; H.V.H Atl., pi. 57, f. 15 ; 

 Type No. 375), plate 15, fig. 494. 



Valves linear-lanceolate, with cuneate apices, median portion sometimes 

 somewhat attenuate; transverse striae robust, 7 to 1 1 in 1 c.d.m. 

 Length, 2 to 5 c.d.m. Breadth, 1 to 15 c.d.m. 



Brackish water. Antwerp ; sometimes fresh water. Brussels Botanical Gardens 

 (Delogne); England; Ireland (O'Meara). 



var. calida. (N. calida Grim. Arct. D., p. 75 ; H.V.H. Atl., pi. 

 59, f. 4 and 5*) plate 15, fig. 495. 



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

 rostrate; sulcus scarcely visible ; striae 17 to 19 in 1 c.d.m. Keel with 

 points rather distinct. Length, 3-5 to 4-5 c.d.m. 



Fresh water (warm). Brussels Botanical Gardens (Delogne). 



var. littoralis Grun. (N. littoralis Grun. ; H.V.H. Atl., pi. 59, 

 f. 1-3* ; in Type No. 190), plate 15, fig. 496. 



Distinguished from the type-form by the well marked carinal dots, and 

 by the compact striation of the valve. 



Fresh or brackish water. Antwerp (Park lake). 



N. debilis (Arnott) Grun. ! (Arct. Diat., P . 68; H.V.H. Atl., pi. 

 57, f. 19-21* ; in Type No. 146), plate 15, fig. 497. 



Valve lanceolate elliptic, with subrostrate apices ; striae very feeble, 1 2 

 to 14 in 1 c.d.m., interrupted in the middle of the valve. Length, 2 to 2*5 

 c.d.m. Breadth, about 1 c.d.m. 



Fresh water. Frahan, Groenendael (Del), Maryhill Bridge, near Glasgow, Scotland (W. 

 Am., No. 847 !). 



N. angustata (W. Sm.) Grun. (Arct. Diat., p. 7; H.V.H. 



Atl., pi. 57, f. 22-24*; in Type No. 475) plate 15, fig. 498. 



BB 



