MAKINE DIATOMS OF THE PHILIPPINE ISLANDS 171 



TRIGONIUM QUINQUELOBATUM (Greville) Cleve 



(Micro. Journ., 1866, p. 83, pi. 9, fig. 21; Schmidt, Atlas, pi. 79, fig. 8.) 



Although I am disposed to agree with Grunow, quoted in the above 

 reference to Schmidt's Atlas, that this is a pentagonal form of T. arc- 

 ticum Cleve, and have so recorded in my Diatoms of the Albatross 

 Voyages, page 291, the arrangement is open to objection. It is worth 

 while to note here that typical specimens of T. arcticum are common 

 in Philippine Islands material and all show the characteristic cluster 

 of small beads within each hexagon of the network, but no trace of a 

 central papilla in the hexagons, or at most a bright spot in the center 

 due to the absence of beads at that point. In contrast to this, 

 T. quinquelobatum, less common but not scarce, has a strong papilla in 

 the middle of each hexagon with no trace of the underlying beading 

 so evident in T. arcticum. There is an unmistakable contrast between 

 the two, both with low magnification and under immersion objec- 

 tives. 



TRIGONIUM RADFORDIANUM (Castracane) Mann 



(Castracane, Chall. Exp., pi. 17, fig. 10.) 



For a discussion of the essential unity of this and T. eulensteinii > 

 see under the latter. 



TRIGONIUM (TRICERATIUM) RADIOLATUM Janisch 



See under Cestodiscus radiolatus. 



TRIGONIUM SCULPTUM Shadbolt 



(Micro. Journ., 1854, p. 15, pi. 1, fig. 4; Schmidt, Atlas, pi. 76, figs. 9-10.) 



As stated above, under T. punctatum, that diatom is a variety of 

 this one. De Toni (Syl. Alg., p. 944) unites them, but under Bright- 

 well's later name (1856), and then confuses the two with T. reticulum 

 Brightwell (1853), following Cleve's mistake in his Diatoms from 

 the West Indian Archipelago, page 16. Van Heurck (Synopsis, pi. 

 109, figs. 7-8) names it T. sculptum, but figures Brightwell's varietal 

 form T. punctatum, which lacks the three rings on which Shadbolt's 

 name was based and which are well shown in the above references. 

 He further implies that the species is really a Biddulphia, from which 

 I dissent, there being no processes at the angles. 



TRIGONIUM ZONULATUM (Greville) Mann 



(Schmidt, Atlas, pi. 77, fig. 33.) 



There is a doubt of the Philippine Islands form belonging to this 

 species. It is exactly figured as above, but it might perhaps better 

 be considered to be a small triangular example of T. latum Greville. 

 The statement made under the latter, that the two are often approx- 

 imately alike, may be here repeated. 



