NAVICULA. 217 



N. serians Breb. (in Kutz. Baa, p. 92, pi. 3c, f. 23 ; H.v.H. Atl, 



pi. 12, f. 7* ; in Type No. 125), plate 4, fig. 196. 



Valve lanceolate. Raphe surrounded by a rather broad hyaline zone, 

 somewhat dilated round the central nodule, which is coarse and round. Striae 

 fine, about 24 in 1 c.d.m., feebly radiate, formed of elongate beads which, by 

 being arranged at some distance apart, appear like irregular longitudinal lines. 

 Length, 6 to 8 c.d.m. Breadth, 1*5 c.d.m. 



Boggy pools. Rare. Calmpthout (Deby) ; Tete de Flandre at Antwerp (H.V.H.) ; Ard. Lig. 

 (De Wild. ). England, Scotland, Ireland, France. 



var. brachysira. (JV. brachysira Breb., H.V.H. Atl. Supp., f. 126*; 

 Types Nos. 126 and 127), plate 4, fig. 197. 



Valve subrhomboidal, with subacute apices. 



Freshwater. Cornimont, Bouillon (Del.). 



N. exilis Grun. (in H.V.H. Atl., pi. 12, f. n and 12* 1 Type No. 

 128), plate 4, fig. 198. 



Valve lanceolate, narrow, with apices rostrate-capitate. Striation, both in 

 structure and direction, analogous to that of N. serians, to which it is allied by 

 infinitesimal gradation (see H.V.H. Atl., pi. 12. f. 10); about 30 striae in 1 

 c.d.m. Length, 23 to 3 c.d.m. Breadth, about 0*5 c.d.m. 



Fresh water. Ard. Lieg. (De Wild.). Ireland. 



N. follis Ehr. (Inf., 1S38, p. 179; Mikr., pi. XVI. 1, f. 14; Donk. 

 Br. D., p. 44, pi. 6, f. 15*; in Type No. 274), plate 27, fig. 771. 



Valve small, cruciform, with costae incurved and gently inflated, apices 

 obtuse. Puncta forming uninterrupted lines in zig-zag in axial illumination, 

 but reduced in oblique illumination to fine stride, radiate, irregularly punctate, 

 about 25 in 1 c.d.m. Raphe thick, central nodule elongate, surrounded by a 

 rhomboidal hjaline space. Length, about 4 c.d.m. Breadth at central 

 inflation, 2 c.d.m. 



Freshwater. Rare. Near Heigham, Norfolk (Kitton). Loch. Kinnord (Davidson). Loch 

 Oich, fossil deposit (Donkin). Loch Canmor, Scotland (Coll. Weissfl. !) Frico, nr. Christiansund, 

 Norway (Coll. W. Arnott !). 



XVI. Formosse. 



Striae everywhere marginal . . . . . N. formosa. 



f Zone feebly dilated ( Valve narrowly elliptic . . N. Liburnica. 



round the central < 



nodule. ( Valve oval, elliptic . . N. latiuscula. 



Stria; not ; 

 marginal. \ y r ,-, , / Dilatation in form of rounded area . N. permagna. 



round the central < -,-., . . -j U i u 



, -, J Dilatation very considerable, sub- 



no e " v, quadrangular . . . N. amphisbaena. 



