MARINE DIATOMS OF THE PHILIPPINE ISLANDS 163 



so common in that genus, and even more so, (2) because of an appar- 

 ent rim or border around the edge of the valve.* This latter, however, 

 is an illusion, due to the appearance of the rows of beading when seen 

 on the curving edge of the valve; for the side (girdle) view shows 

 that no such border or rim exists. It also shows the above-mentioned 

 sinus where the valve joins the girdle, a construction never found in 

 Stictodiscus. This is therefore an illustration of the desirability of 

 obtaining both face and girdle views of such diatoms. Both valves 

 are alike in their shape, a fact which would also exclude this from 

 Stictodiscus if we accept the generally expressed statement that the 

 two valves of Stictodiscus differ in their convexity. (See Van Heurck's 

 Treat. Diat., p. 506.) This, however, is not to be relied upon- 

 St. californicus Greville, for example, rarely has its two valves of differ- 

 ent convexity. This new species is well distributed and fairly abun- 

 dant at the Philippine Islands. 

 Type.— Cat. No. 43693, U.S.N.M. 



TRIGONIUM DIAPHANUM, new species 



Plate 37, fig. 3 



Valve only slightly convex, but near the margin turning rapidly 

 downward to form a deep vertical flange or rim that joins the girdle 

 of the frustule; three to five angled, the sides between the angles 

 convex, except occasionally in triangular specimens, where they are 

 practically straight; surface of the valve covered with small beads in 

 radiating rows, gradually enlarging from the center to the sides, where 

 they sometimes become imperfectly square or hexagonal from pres- 

 sure, the separate beads having each a minute central dot (prickle?), 

 the larger polygonal ones a more or less rugose appearance; the bead- 

 ing of the three to five produced and rounded angles is finer and more 

 closely se t an that of the res of the val e; at the center is a con- 

 spicious cluster of small spines grouped into an im erfect rosette- or 

 sometimes a ring. Under moderate magnification this diatom has a 

 delicate, lacy appearance. 



Diameter (apex of angle to middle of opposite side) 0.135-0.231 

 mm. 



This species is the unnamed figure in Janisch's Report of the 

 Gazelle Expedition, plate 9, figure 1. From the fact that his photo- 

 graph was made from a broken specimen we may infer that it was 

 rare in his material. It is remarkably abundant in some of the 

 Philippine Islands dredgings, the three, four, or five angled forms being 

 often found together in the same strewing. The four-angled forms 

 generally predominate. Although this species is thin and gossamer- 

 like it is very conspicuous in a dry strewing, not only because of its 



