NITZSCHIA. 399 



ANALYSIS OF SPECIES. 



'8 to 12 faint carinal dots in i c.d.ra. ; valve showing a slight inflexion at 



the median portion . . . . . . N. linearis. 



.5 to 7'S ver y robust carinal dots in i c.d.in. ; valv2 without median inflexion N. vitrea. 



N. linearis (Ag.) W. Sm. ! (s.b.d., i., p. 39, pi. 13, f. no, and 



Supp., pi, 31, f. no ; H.V.H. Atl, pi. 67, f. i3*-i5 ; Type No. 404), plate 

 16, fig. 542. 



Valves longly linear, almost in the form of a boat, with apices rounded at 

 the external, and attenuate at the internal portion. Keel, 8 to 10 dots in 1 

 c.d.m., the two median more distant than the others, the space between 

 generally corresponding with a small inflexion of the valve. Stride, 29 or 30 

 in 1 c.d.m. ; finely punctate. Length, 7 to 18 c.d.m. Breadth of valve, 

 about - 5 c.d.m. 



Fresh water. Rather common throughout Europe. 



var. tenuis Grun. (H.V.H. Atl., pi. 67, f. 16; Type No. 406), 



plate 16, fig. 543. 



Valve narrow (-4 to 7 c.d.m.). Keel, n or 12 dots in 1 c.d.m. Striae 

 more than 30 in 1 c.d.m., generally interrupted at the median portion of 

 the valve. Girdle face "4 to '9 cd.m. Length, 7 to 15 c.d.m. 



Fresh water. Common. 



N. vitrea, Norman ! (T.M.S., 1861, i, n.s., p. 7, pi. 2, f. 4 ; 

 H.V.H. Atl., pi. 67, f. 10*), plate 16, fig. 544. 



Differs from the preceding species by the carinal dots (5 or 6 in 1 c.d.m.) 

 being often coarser and quadrangular, rounded, and by the girdle face being 

 very broad, sometimes constricted and by the connective zone having numerous 

 plicae. Striae, 20 to 22 in 1 c.d.m. Length, 6 to 13 c.d.m. Breadth of 

 valves, "5 c.d.m. ; breadth of girdle face, up to 2^5 c.d.m. 



Brackish water. Scheldt at Antwerp. Ard. Lieg. (Dr. Wild.). Hull, England (Norman), 

 Scotland (H.V.H. Type No. 382). 



forma major. (H.V.H. Atl., pi. 67, f. 11*; Type No. 402), plate 

 16, fig. 545. 



Valves up to 12*5 c.d.m. in length and 1*25 c.d.m. in breadth, with 17 

 striae in 1 c.d.m. 



var. salinarum Grun. (Arct. Diat., p. 94; H.V.H. Atl., pi. 67, f. 

 12*; in Type No. 431), plate 16. fig. 546. 



Smaller than the type-form (3*5 to 8 - 5 c.d.m. in length), valves broad 

 (:$ to - 9 c.d.m.), and striae narrower (28 to 30 in 1 c.d.m.). 



Brackish water. Ostend (Grunow). 



