166 BULLETIN 100, UNITED STATES NATIONAL MUSEUM 



TRIGONIUM EULENSTEINII (Grunow) Mann 



Plate 37, fig. 4; plate 38, figs. 1, 2, 3. 



(Schmidt, Atlas, pi. 75, figs. 6-7; pi. 81, fig.13.) 



Triceratium eulensteinii Grunow, Schmidt, Atlas, pi. 75, figs. 6-7. 

 Stictodiscus eulensteinii (Grunow) Castracane, Chall. Exp., p. 116. 

 Triceratium portuosum Janisch, Schmidt, Atlas, pi. 81, fig. 13; T. eulensteinii, 



var. inornata A. Schmidt. 

 Stictodiscus bicoronatus Castracane, Chall. Exp., p. 120, pi. 6, fig. 5; pi. 13, 



fig. 2. 

 Stictodiscus radfordianus Castracane, Chall. Exp., p. 118, pi. 17, fig. 10, 

 Stictodiscus anceps Castracane?, Chall. Exp., p. 116, pi. 1, fig. 5. 

 Triceratium multiplex Janisch, Schmidt, Atlas pi. 75, fig. 1; pi. 81, fig. 14. 

 Stictodiscus multiplex (Janisch) Castracane, Chall. Exp., p. 116. — Truan 



and Witt, Diat. Hayti, p. 21 pi. 5, fig. 7. 

 Triceratium (Biddulphia) heteroporum Grunow, Van Heurck, Synopsis, 



pi. 112, fig. 2. 

 Triceratium galapagense Cleve, New and Little Know Diat., p. 25, pi. 6, 



fig- 72. 



Through the good fortune of having a large number of gatherings 

 from the Philippine Islands in which nearly all the above are more 

 or less abundant I have been able to compare these apparently 

 diverse forms. I find they are unquestionably only differently shaped 

 phases of the same general type represented by Triceratium eulen- 

 steinii Grunow. It is very possible that Stictodiscus anceps Castracane 

 and the second figure of Stictodiscus bicoronatus Castracane in the 

 Report of the Challenger Expedition, plate 13, figure 2, may together 

 represent a second closely allied group. I have not seen a sample 

 of T. lieteroporum Grunow, which comes from fossil St. Monica mate- 

 rial; but judging from the illustration in Van Heurck's Synopsis, plate 

 112, figure 2, unfortunately without description, it is specifically 

 identical with Castracane's Stictodiscus bicoronatus. The most aber- 

 rant example of this group is the biangular form here illustrated, which 

 is rather abundant in the Philippine Islands. Such biangular forms 

 of normally triangular diatoms are not at all uncommon; as for 

 example, the biangular form of Entogonia davyana Greville, called 

 u Heibergia barbadensis" Greville, and the biangular form of Trigonium 

 arcticum (Brightwell) Cleve, called Biddulphia balaena (Ehrenberg), 

 var. arctica. All the diatoms named with the present species have 

 certain peculiarities in common and which also distinguish them from 

 other diatoms. They are marked with small but strong beads, rather 

 loosely dispersed except near the margin of the valve, where they are 

 more closely set and arranged in definite rows at right angles to the 

 edge; at the angles of the valve, whether two or many, the beading 

 is smaller, more compact, and is arranged somewhat f anwise. In the 

 center of each of the larger beads is a minute dot or prickle, and 

 where this is prominent the bead is elongated radially as to the center 

 of the valve and the central prickle seems to divide it into twin halves. 



