MARINE DIATOMS OF THE PHILIPPINE ISLANDS 119 



tortuous, especially near the center, its outer ends curved and reach- 

 ing the apices of the valve, its inner ends well separated; in side 

 (girdle) view the sunken stauros shows as a deep central notch. 



Length, 0.090-0.141 ; width, 0.029-0.035; lines, 10.6-11 in 0.01 mm. 



Compare with N. impleta Cleve and Grove (Le Diatomiste, p. 58, 

 pi. 1, figs. 1-2) from Macassar Straits, and N. crucifix Tempere and 

 Brun, Diatomees du Japon (p. 42, pi. 7, fig. 10) fossil at Sendai, 

 Japan. 



Type.— Cat. No. 43660, U.S.N.M. 



NAVICULA RHOMBICA Gregory 



(Micro. Journ., 1856, pi. 5, fig. 1, Cleve, Nav. Diat., vol. 1, p. 152.) 



There is some question as to this species being a true Navicula, 

 chiefly because of its peculiar rhaphe, which is heavy, rodlike, with 

 ends terminating at some distance from the apices of the valve. 

 Nevertheless, as no other assignment seems to be more satisfactory, 

 this one is provisionally adopted. Specimens from recent dredgings 

 from the Philippine Islands as well as from other localities do not 

 agree exactly with Brun's form from the fossil deposit at Sendai 

 Japan, Navicula (ScMzonema) japonica (Brun) Cleve (Brun Espec. 

 Nouv., pi. 14, fig. 6), but the two can hardly be separated. Some- 

 what similar is Brebissonia weisflogii Grunow (Cleve, W. I. Diat., pi. 

 l,fig. 9). 



NAVICULA ROBUSTA Grunow 



(Schmidt, Atlas, pi. 50, figs. 1-2.) 



NAVICULA SAMOENSIS Grunow 



(Schmidt, Atlas, pi. 50, figs. 43-44.) 



NAVICULA SEDUCTILIS A. Schmidt 



(Schmidt, Atlas, pi. 2, fig. 35.) 



That this is a mere variety of N. lyra Ehrenberg, as claimed by 

 O' Meara, De Toni, and others, may be doubted. 



NAVICULA SEMISTAUROS, new species 



Plate 28, fig. 5 



Valve convex, spindle-shaped, with narrow, rounded apices, unsym- 

 metrically marked on its two sides ; one side having closely set diag- 

 onal beaded lines, broken here and there by wider spacing between 

 the beads and also by single beads being larger than the rest, these 

 two irregularities producing a wavy appearance in the markings ; a 

 central stauros is also unsymmetrical, its half on this side being very 

 small, while on the other side it is strong, flaring, and reaches about 

 halfway to the margin ; the rows of beading on this last-mentioned 

 side having the flaring half stauros, are even more irregular as to the 



