400 



NITZSCHIA. 



var. recta (A 7 , recta Hantzsck; H.V.H. Atl., pi. 67, f. 17 and 18*), 

 plate 16, fig. 547. 



Keel somewhat eccentric, with 6*5 to 7*5 dots in 1 c.d.m., the median 

 more approximate than the others. More than 30 striae in 1 c.d.m. 

 Frustules narrower than the preceding variety, about "6 to 1*2 c.d.m. in 

 breadth). 



Fresh (?) and brackish water. Ard. Lieg. (De Wild.) ; England (H.V.H. Type No. 96). 



Group 21. LanceolaT/E. 



Valves lanceolate, linear lanceolate, or more rarely oval. Keel 

 very eccentric, with dots not elongated. 



ANALYSIS OF SPECIES. 



f Connecting zone very broad and strongly plicate 

 1 



I Median carinal dots somewhat more distant than the others 



I 



f Valves with apices rostrate-capitate 



o 



u 

 u 



a 

 G 



o 



c 

 c 

 o 

 U 



Carinal 



dots all 



equidistant 



I 



Valves 



with 



apices 



not 



capitate. 



. N. lanceolata. 



N. subtilis. 

 - N. microcephala. 

 f Strice conspicuous (16 to 17 in 1 c.d.m.) N. amphibia. 



Strife 



indistinct, 



more 



than 20 



in 1 c.d.m. 



I 



Valves linear, abruptly 

 produced subrostrate ; 

 carinal dots well 

 marked ; strife very 

 delicate (about 30 in 

 1 cd.m.) . . N 



Valves lanceolate, con- 

 siderably rostrate ; car- 

 inal dots faint ; strife 

 very delicate (30 to 36 

 in 1 c.d.m. ) . , N. 



Valves narrowly lanceo- 

 late or linear, more or 

 less rostrate ; carinal 

 dots faint ; strife more 

 visible (20 to 22 in 1 

 c.d.m.) 



communis. 



Palea. 



N. Frustulum. 



Carinal dots not visible 



Strife invisible, 13 conspicuous carinal 

 t dots in 1 c.d.m. . . . N. 



N. 



ovalis. 

 Delognei. 



N. lanceolata, W. Sm. (S.B.D., i., pi. x 4 , f. n8; h.v.h., pi. 



68, f. 1 and 2*; Type No. 407), plate 17, fig. 548. 



Valve narrowly lanceolate, with acute apices. Keel very eccentric, about 

 5 to 7 dots in 1 c.d.m., all equidistant. Striae fine, about 30 in 1 c.d.m. 

 Girdle face linear, strongly inflated at the median portion, with obtuse apices 

 and strongly plicate connecting zone. Length, up to 20 c.d.m. Breadth of 

 valve, 175 c.d.m. 



Brackish water, England (W. Sm., Norman, Stolt.), Ireland (O'Meara). 



