MARINE DIATOMS OF THE PHILIPPINE ISLANDS 115 



it is suddenly widened and close to the two ends where it is rapidly 

 narrowed and disappears, leaving a small triangular hyaline space 

 beyond each end of the rhaphe; rhaphe straight, strong, sharply 

 hooked toward the same side at the outer ends, the inner ends well 

 separated; short and similar rows of beads run parallel to the rhaphe 

 on either side, they are narrowest at the outer ends and widest at 

 the center of the valve; the rest of the valve is loosely spattered with 

 larger but shadowy beads, showing a tendency to a radial arrangement. 



Length, 0.079-0.125; width, 0.059-0.087; 3.7 lines in 0.01 mm. 



Very clearly this brilliantly sculptured diatom is in that large group 

 of Naviculae of which N. excavata Greville and N. caribaea Cleve are 

 typical. But when compared, it can not be united as specifically 

 identical with any of them, however difficult it might be to draw a 

 clear line of distinction between them by means of an unillustrated 

 description. It is the most abundant Navicula in the Philippine 

 dredgings, including those from the Sulu group. It is of unvarying 

 uniformity as to its markings and all specimens are relatively large. 



Type.— -Cat. No. 43655, U.S.N.M. 



NAVICULA PINGUIS Mann 



(Mann, Diat., Alb. Voyages, p. 350, pi. 53, fig. 5.) 

 The original type form was from Bering Sea. 



NAVICULA PLICATULA Grunow 



Plate 24, figs. 8-9 



(Cleve, Nav. Diat., vol. 1, pi. 3, fig. 28; Castracane, Chall. Exp., pi. 28, fig. 13, 

 unnamed.) 



This is the unnamed Navicula in Report of the Challenger Expedi- 

 tion, plate 28, figure 13, from Tahiti. It is also very probable that 

 N. parallela Castracane shown in the same work, plate 28, figure 12, 

 is the same species, although the two figures seem to be quite differ- 

 ent. For in Philippine Islands material I have found all transi- 

 tions between these two, both as to straight or undulating rhaphe and 

 as to bluntly oval or appressed apices. A study and measurement 

 of a large series indicates beyond much doubt that this difference is 

 merely a varietal one. The average length of my specimens is 0.084 

 to 0.138 mm., and the width from 0.031 to 0.038 mm. All are 

 strongly convex, very diaphanous, with identical markings, namely, 

 very fine transverse beaded lines; all have about 18 lines in 0.01 mm., 

 measured midway between center and apex of valve; all have a 

 shadowy line parallel to the margin running midway between the 

 margin and the center on eace side of the rhaphe. This smaller cen- 

 tral oval or ellipse, thus dimly marked out, Cleve refers to as a " slight 

 depression." If therefore plate 28, figure 12, and plate 28, figure 13, 

 as shown in the Report of the Challenger Expedition, are identical 



