MARINE DIATOMS OF THE PHILIPPINE ISLANDS 167 



This is usually observable in T. multiplex, Stictodiscus radfordianus, 

 Stictodiscus bicoronatus, and the unnamed biangular form here figured, 

 and is very evident in my photograph of the triangular T. bicorona- 

 tum (Castracane) Mann. It would seem to be evident also in 

 T. heteroporum Grunow, judging from the Van Heurck figure. In addi- 

 tion to the beading, the surface of the valve is more or less covered 

 with very fine puncta that give to it a dusty appearance, but which 

 is absent in a little ring around each of the beads. This is very gen- 

 erally seen in Stictodiscus bicoronatus and is so noted and figured by 

 Castracane; in T. multiplex, as represented in Schmidt's Atlas, plate 

 75, figure 1, and plate 81, figure 14, in my photograph of Stictodiscus 

 bicoronatus and in Triceratium heteroporum, because of which the 

 latter specific name was selected. Traces of this dusty spattering 

 are also more or less observable in T. eulensteinii and Stictodiscus 

 radfordianus. There are two other specific marks that are more in- 

 constant; one is a single or double rosette of beads or lines at the 

 center. It is generally prominent in T. eulensteinii (Schmidt, Atlas, 

 pi. 75, figs. 6-7), but is sometimes lacking (pi. 81, fig. 13) a phase 

 called for this reason var. inornata. In T. multiplex it is frequently 

 obscure or absent, but is strongly marked in Schmidt's Atlas, plate 

 75, figure 1 , and dimly so in Schmidt's Atlas, plate 81 , figure 14. In the 

 biangular form it is usually conspicuous, sometimes a single ring, some- 

 times a double one. It is very evident in T. heteroporum as a single 

 ring, in Stictodiscus bicoronatum as a double ring, whence the name. 

 It is lacking in T. galapagense Cleve. The other inconstant factor is 

 the set of watery radiating lines, sometimes straight and some- 

 times anastomosing. They are usually quite strong in T. eulensteinii. 

 This is the case in Schmidt's Atlas, plate 75, figure 6 ; but in plate 

 75, figure 7, they are more indistinct and even more so in plate 

 81, figure 13. In Castracane's type figure of St. bicoronatus, Chal- 

 lenger Expedition, plate 6, figure 5, they are evident; but in his 

 second figure, plate 13, figure 12, they are wholly wanting. In Cas- 

 tracane's figure of St. radfordianus, Challenger Expedition, plate 17, 

 figure 10, they are rather dim, but in my specimens of this form from 

 the Philippine Islands they are very strong. They are also well 

 marked in T. galapagense Cleve. I have never found more than mere 

 traces of them in the biangular form here figured. No hint of them 

 is given in Van Heurck's figure of T. heteroporum Grunow. 



It will be seen from the forgoing that we have here a group of 

 diatoms well defined from the species outside of the group, but with 

 no constant mark of distinction between each other. Nevertheless, 

 we find the name eulensteinii given to such specimens as have an 

 undulate margin, radfordianus to such polygonal forms as have prac- 

 tically straight sides and slightly protruded angles, multiplex to those 

 with straight sides but not protruded angles, bicoronatus to triangular 



