NITZSCHIA. 403 



N. amphibia Grun. ! (Arct. Diat., p. 68 ; H.V.H. Atl., pi. 68, f. 

 15-17*; Type No. 40S), plate 17, fig. 563. 



Valves longly linear, or lanceolate and short, with apices produced sub- 

 rostrate, 7 to 8 carinal dots, and 16 to 17 very distinct striae in 1 c.d.m. 

 Length, 2 to 4 - 5 c.d.m. Breadth of valves, about '5 c.d.m. 



Fresh water. Common. 



N. Frustulum (Kiitz.) Grun.! (Arct. Diat, p. 98; H.v.H. 



Atl., pi. 68, f. 28 and 29* ; Type No. 410 var. tendla), plate 17, fig. 564 



Valves narrowly lanceolate or linear, with 9 to 1 1 carinal dots and 20 to 

 22 striae in 1 c.d.m. Length, 2 to 4 c.d.m. Breadth, about 1 c.d.m. 

 Brackish water. Ard. Lieg. (De Wild.). 



var. minutula. (H.V.H. Atl., pi. 69, f. 5*), plate 17, fig. 565. 



Small, very narrowly linear, with 12 or 12*5 carinal dots and 30 or 31 

 stria; in 1 c.d.m. 



Groenendael (Delogne). 



var. perpusilla Rabenh. (H.V.H. Atl., pi. 69, f. 8*), plate 17, 

 fig. 566. 



10 to 12 carinal dots and 23 or 24 stria; in 1 c.d.m. Frustules often 

 united in short filaments. Length, 1*5 to 4^3 c.d.m. Breadth of valves, 

 about - 4 c.d.m. 



Common. 



N. OValis Arnott ! (Manuscript H.V.H. Atl., pi. 69, f. 36*; Type 

 No. 414), plate 33, fig. 880. 



Valves very broad, longly oval, with rounded apices, and strias excessively 

 delicate, scarcely visible with the best objectives; about 13 well marked 

 carinal dots in 1 c.d.m. Girdle face narrow. Length, 1*5 to 2 c.d.m. 

 Breadth of valves, about '5 c.d.m. 



Fresh water. Durham, England (Coll. \V. Arnott! No. 1892 and 190). 



N. Delognei Grun. ! (H.v.H. Atl. Supp., f. 38*; Type No. 106), 

 plate 17, fig. 567. 



Valves lanceolate, linear, somewhat rostrate-apiculate. Carinal dots indis- 

 tinct ; transverse striae about 19 in 1 c.d.m., strongly punctate. Breadth of 

 valve about 1*5/*. Length, about 1*5 c.d.m. 



Fresh water. Brussels (Delogne). 



This species may easily be mistaken at first sight for a Sy?iedra, which 

 should have no trace of a pseudo-raphe. 



