384 



TRYBUONELLA. 



Group i. Tryblionella (W. Smith partimj Grunow. 



Fig. 125. 



Nitzschia punctata 



( Tryblionella). 



Keel very eccentric, with dots almost 

 always indistinct, generally equal in number 

 to those of the striae. Valves generally sulcate, 

 undulate. 



I unite with this group, group 4 (Psenrfo- 

 Tryblionella), which is only distinguished from it 

 because the carinal dots are well marked. 



ANALYSIS OF SPECIES. 



{ Valve showing strife formed of coarse puncta 



. N. punctata 



Valves not 



with 



coarse 



puncta. 



f Valves with strife very fine at the centre of the valve ; stria; 



terminating at the margins in a double row of puncta . N. navicularis. 



(' Stria; traversing the entire linear valve . N. angustata. 



Stria; Valve f Valves with robust stria; ; sul- 



not showing cus not hyaline . . N. Tryblionella. 



as above. a 



median | Valve very small ; stria- very 



^ sulcus. (_ delicate; sulcus hyaline . N. debilis. 



N. navicularis (Breb.) Grun. ! (Arct. Diat., p. 67 ; H.V.H- 



Atl., pi. 57, f. 1* ; Type No. 371), plate 15, fig. 490. 



Valves elliptic-lanceolate, with striae (7 in 1 c.d.m.), fine at the central 

 portion of the valve, terminating towards the margins on each side in a double 

 row of puncta. Length, about 3*5 c.d.m. 



Marine. Ostend (Deby.) ; Scheldt at Antwerp (H.V.H.) ; England (Norm., W. Sm., Comber, 

 Dickie) ; France (Br6b.). 



N. punctata (Sm.) Grun. ! (Arct. Diat., p. 68; H.V.H. Atl., pi. 

 57, f. 2* ; Type No. 372), plate 15, fig. 491. 



Valve elliptic-lanceolate, with apices somewhat rostrate ; striae 7 to 9 in 

 1 c.d.m., formed of coarse puncta. Length of valve, 2*5 to 3^5 c.d.m. 

 Breadth, 1 to 3 c.d.m. 



Brackish water. Ostend (Deby); Antwerp; England (\V. Sm., Stolt., Comber) 

 Holland ; Denmark. 



France 



