NAVICULA. 



223 



N. semilla Ad. Schm. (Nordsee, p. 91, pi. 2, f. 47*; JV. subdivisa 

 Grun., Arc. Diat, p. 29, pi. i, f. 20), plate 27, fig. 772. 



Is only differentiated from N. consimilis by its smaller size, by its stride 

 being more approximate (19 to 21 in 1 c.d.m.) and by the marginal sulcus 

 being less apparent. 



This form has been recorded from Normandy and the Baltic. 



XX. Americanae. 



Striae marginal throughout, and much shortened at the median portion of the 

 v al v, 5 .......... N. Americana. 



N. Americana Ehr. (Mikr., P i. 11. 2, f. 16; h.v.h Atl., pi. 12, 



f. 37*; Type No. 138), plate 5, fig. 221. 



Valve linear obbng, with rounded apices, slightly constricted near the 

 middle. Raphe robust, surrounded by a hyaline zone, occupying the moiety 

 of the valve and further dilated round the central nodule, which is robust 

 and marked by one or two pore-like puncta near its lower third. Marginal 

 striae feebly radiate, finely punctate, 16 in 1 c.d.m. Length, about 9*5 c.d.m. 

 Breadth at the median constriction 2*5 c.d.m. ; at the broadest portion 275 

 c.d.m. 



Fresh water. Very rare. Antwerp (Belleroche !), Ireland (OM.), Loch Kinnord, Scotland 

 (Davidson). 



XXI. Bacilleae. 



Valve linear, 



without any 



considerable 



inflations. 



r 



f No pseudo-stauros, terminal nodules 



Terminal nodules 

 straight, not - 

 prolonged la- 

 terally . 



surrounded by a considerable hya- 

 line area 



I A pseudo-stauros, terminal nodules 

 without any considerable hyaline 

 L area ..... 



Terminal nodules straight, comma-like 



Terminal nodules 

 curved later- 

 ally like a 

 crook 



Valve broadly linear, central nodule 

 surrounded by a considerable hya- 

 line area .... 



N. Bacillum. 



N. bacilliformis. 

 N. subhamulaba. 



N. pseudo-bacillum 



Valve narrowly linear, often very 

 feebly inflated at the median por- 

 tion ; no considerable hyaline area N. laevissima. 



Valve f Striae almost submarginal, no false stauros, terminal 

 inflated in nodules curved like a crook unilaterally . . N. Hebes. 



the middle -1 



and at the | Striae extending up to the raphe a false stauros ter- 



apices. I, niinal nodules curved like a crook bilaterally . . K. Pupula, 



