106 BULLETIN 100, UNITED STATES NATIONAL MUSEUM 



the width of the valve and bisected by the rhaphe line and extending 

 clear to the ends of the valve, is covered by equally closely set but 

 much smaller beading, arranged in double rows, in zigzag formation, 

 each double row continuous with the coarser single rows of the out- 

 side area and extending inward to the rhaphe line; the rhaphe is 

 heavy, reaching to the ends of the valve; the hyaline area of the cen- 

 tral nodule is small and oval. 



Length, 0.13; width, 0.053; lines. 6.5 in 0.01 mm. 



This species belongs to the Navicula fusca group. Its outer bead- 

 ing is similar to that species, but much coarser and denser; its inner 

 double beading is similar to that of N. smithii Brebisson. There is a 

 great confusion between these two latter and N. aestiva Donkin. The 

 muddle is not at all helped by Cleve's attempt in Naviculoid Diatoms, 

 volume 1, page 93, where he excludes the figure and description of N. 

 fusca in Donkin's British Diatoms, page 7, plate 1, figure 5, making it 

 Diploneis borealis (Grunow) Cleve and includes the utterly irrelevant 

 N. subfusca Pantocsek, var. oamaruensis Cleve, which he figures on 

 his plate 2, figure 3. A careful study of these related forms, in which 

 the Philippine Islands gatherings are quite rich, makes it evident that 

 we have three or perhaps four well-marked types. In N. smithii, 

 a species of broadly oval shape, the beading is always in double rows 

 between costal lines, both in the outer portion of the valve and in 

 the inner elliptical portion, the double beading of the latter however 

 being fainter. In N. aestiva the beading is delicate, in single rows 

 without costal lines, both in the outer portions and in the elliptical 

 central portion. In N. fusca (based on "N. smithii var. B. fusca 

 Greg." in Diatoms of the Clyde, p. 486, pi. 9, fig. 15) the beading is 

 also in single rows in both inner and outer portions, but so much 

 more massive than that of N. aestiva that the two can only with 

 difficulty be taken as variations of each other; the central part of 

 N. aestiva being also much less angular in outline than that of N. fusca. 

 In the new species here presented we have a fourth form, where the 

 beading of the outer portions is even more massive than in N. fusca, 

 while the strongly contrasting central portion is covered with double 

 rows of fine beading separated by costal lines. That this never 

 occurs in N. fusca is shown by the careful drawing by Tuff en West of 

 the original type in Diatoms of the Clyde, plate 9, figure 15, in the 

 figure in Donkin's British Diatomaceae, plate 1, figure. 5, also by 

 Tuff en West; in the figure in Schmidt's Atlas, plate 7, figures 1-4; 

 in Peiagallo's Diatom'ees de France, plate 20, figures 6-7; and in the 

 express statement of Gregory above cited; in the statement by Ralfs 

 in Pritchard's History of Infusoria, page 899; in that of Donkin's 

 British Diatomaceae, page 7 ; and that of Do Toni in Sylloge Algarum, 

 page 87. 



Type.— Cat. No. 43649, U.S.N.M. 



